Page images
PDF
EPUB

66

In point of fact, as may be seen on Dr. Hann's charts for January and July, in the new edition of Berghaus's Physical Atlas," the diversion of the trade-winds of the Gulf of Mexico, northward up the Mississippi valley takes place only in the summer, and is an effect of the same agency, viz. the heating of the northern continents, that breaks up the high-pressure zone of the northern tropic into two anticyclones, one in each of the great oceans, and it is the juxtaposition of the Atlantic anticyclone and the Mexican cyclonic depression that determines the course of the winds and the resulting rainfall. To judge from the case of the Western Ghats, we think it may be safely concluded that, if there were no mountain-chain to the west of the Gulf, the results would not be greatly different. All the other instances quoted, illustrative of the diversion of great currents by mountain-chains, except such as are purely local, appear to us to be really due to other and similar causes.

In treating of the monsoons, Prof. Ferrel points out with perfect justice that their strength depends on the form of the land, and that they blow strongly only where the interior of the country is high and mountainous. But when he adduces Persia as an illustration of the negative case, we are unable to admit its relevancy. At p. 199 he observes :

the Arabian Sea; but chiefly in the fact that any tendency that the heated highlands of Persia may have to create such an indraught is overborne by the stronger set towards India. For the latter country reaches far down into the tropics, and the centre towards which the mon soon blows must be determined by the resultant of all the temperature gradients of the whole heated region. An eastward direction having been given to the monsoor at the outset, its strength in that direction is greatly increased by the energy set free in the Indian monsoon rainfall.

This question is one of more than theoretical importance. These west winds of Persia and Afghanistan are the dry winds of Northern and Western India, and when they prevail beyond their normal limits, over the north of the Arabian Sea and a great part of India itself, to the exclusion of the rain-bearing current, they bring the drought and consequent dearth that have made India so disastrously notorious for its famines. Possibly, the explanation of their abnormal extension may be looked for in those oscillations of the great polar cyclonic systems to which Prof. Ferrel alludes at p. 339 of his work.

Cyclones and tornadoes are treated at great length. each of these subjects occupying more than one hundred pages of the book; and in connection with the latter is which has hitherto been less understood than almost any given the author's theory of the formation of hail, a subject other phenomenon of the atmosphere. It will be best given in the author's own words:

"In accordance with the preceding view of the principal cause of monsoons and land and sea breezes, it is seen from observation that all the great monsoons and the strongest land and sea breezes are found-the former in countries and on oceans adjacent to high mountainranges, and the latter along coasts with high mountains "In the ascending current of a tornado, as in that of in the background. Neither the heated interior in sum- the equatorial calm belt, or of a cyclone, the rain-drops mer of the Great Sahara of Northern Africa, nor of are formed down in the cloud region, and carried upward Arabia and Persia, which is considered the warmest re- until they become too large to be supported by the current gion on the globe, causes, during this season of the year, and so fall to the earth. . . . In a tornado, however, the any great indraught of air. It is true that at this season ascending current is often so strong that the rain is the north-westerly winds prevail a little more on the supported until, by the blending of the small drops by north-west coast of Africa and the ocean adjacent, due, no coming in contact, very large drops are formed, and the doubt, to the influence of the highly-heated desert of strong ascending currents often extend so high that these the Sahara; but over Arabia and Persia the north-west large drops are carried away up into the region of freezing winds continue to blow almost incessantly, during June temperature. . . . There they are frozen, and after having and July, away from the interior toward the Arabian been carried up and outward above to a distance from the Sea... The monsoon influence, therefore, of countries centre, where the ascending current is not strong enough mostly level, without an elevated interior, however highly... to keep them up, they slowly descend, and receiving they may become heated in summer or cooled in winter, is not very great."

But the interior of Persia is a part of the great tableland of Iran, and, to quote the description of Sir Oliver St. John, "its average height above the sea may be about 4000 feet, varying from 8000 or higher in certain of the outer valleys to not more than 500 in the most depressed portions of its centre." Its average elevation is therefore much greater than that of the interior of India, very much greater than that of the Indo-Gangetic plain, which is the goal of the Indian monsoon, and, as a glance at the map will show, it is not deficient in mountains. The explanation of the fact that, instead of attracting the monsoon from the Arabian Sea, it is itself swept by north-west and west winds-blowing, not, indeed, towards the Arabian Sea, but towards the lower Indus valley-must then be sought for elsewhere. The true explanation appears to us to lie in a combination of causes. Partly, perhaps, in the latitude, which brings it within the zone of the strong easterly current of extra-tropical regions, which, by its right-handed pressure, must resist any indraught from

additions of ice as they fall, as long as their temperature remains below zero, . . . they finally fall to the earth as solid hailstones"

The concentric coatings so commonly observed in large hailstones are explained by these hailstones being carried again and again into the vortex by the strong indraught in the lower part of the storm-cloud, the theory being that every hail-cloud is a tornado, although it may not reach down to the lower atmosphere. The vapour being condensed as water in the lower part of the vortex, which is frozen at a higher level, and as snow in the upper part. each pair of coatings indicate an additional ascent through the storm-cloud. This view, which, even at first sight, seems far more reasonable than any previous theory, has received unexpected confirmation from the experience of more than one adventurous balloonist, more especially that of Mr. John Wise, whose fate it was to be drawn seven times successively into the vortex of a hail-cloud, and carried up repeatedly until the balloon was thrown out at the top. The account is, unfortunately, too long for extracting.

[blocks in formation]

Atlas deutscher Meeresalgen. Heft I. Von Dr. J. Reinke
Berlin: Paul Parey, 1889).

THE
HE German Government, operating through the
Kommission zur wissenschaftlichen Untersuchung
der deutschen Meere, has undertaken to bear the cost of
producing this sumptuous "Atlas" in the interests of
fishery, and students of phycology have to thank an eco-
Comic aspect of their study for a very remarkable addition
to the literature of it. Similarly, we are indebted to the
United States Fish Commission for the publication of
Frd, Farlow's "New England Alga."

It may be said at once that Dr. Reinke's "Atlas"
a success in every way, its level being that of
Hornet and Thuret's "Études Phycologiques." From
the point
of view of technique, the plates are splendidly
done, and the rest of the publication is worthy of them.
This first part contains twenty-five quarto plates, and the
text belonging to them consists of descriptions of the
Vr figured and special descriptions of the illustrations.
Speaking not merely from an inspection of the book, but
from a knowledge of the material of much of it com-
municated by Dr. Reinke to the British Museum, I do
not hesitate to state that every one of these figures has
great value to phycologists. They are not mere portraits
of Alge, taken from specimens more or less at haphazard,
as is too much the fashion, but they represent faithfully
characteristic stages in the development of the organisms
point. What is commonly termed "microscopical
detail" fills the "Atlas," and one can hardly imagine it
better done. In this portion the author (who has had the
assistance of Dr. F. Schutt and P. Kuckuck) deals
prominently with the Phæophyceae, which, it is well
known, are his particular study at present.
Many of
them are types of his own discovery, and generally
unknown to workers in this field until this satisfactory
introduction to them. Since they are of special import-
ance to our native phycologists as Alga of the North Sea
and Baltic, a list is given of them :-

Mert., var.

Flustra, Rke., Cladophora pygmæa, Rke., Pringsheimia scutata, Rke.

It may be anticipated that a fair number of the novelties among these so-called "German Algæ" (the title reminds one of the “Protestant trout ") may be found on our own coasts.

It should be mentioned that more systematic detail with reference to many of these is to be found in the author's "Algenflora des Westlichen Ostsee" (Berlin, 1889).

The author very properly calls attention to the fundamental importance of a thorough knowledge of marine Algae to fishery, since the plant world prepares by its organs of assimilation the food of the animal world in the sea. The German Commission deserve the highest praise for the enlightened view of their functions embodied in this undertaking, and no biologist will grudge the warmest encouragement to Dr. Reinke in his work. It is anticipated that the book, when complete, will contain a hundred plates, with the accompanying text. In these days, when the most unmitigated rubbish frequently comes to us with highly pretentious illustrations, the student has learned to be on his guard against "prepossessing appearances." No plate manufacture, however, can produce the welcome impression of weight and importance stamped on this "Atlas," gained to a great extent by the fact that Dr. Schütt and Herr Kuckuck, who have drawn the plates, have given us the work of skilful botanists, and not that of draughtsmen only.

OUR BOOK SHELF.

G. M.

Die mikroskopische Beschaffenheit der Meteoriten erläutert durch photographische Abbildungen. Von G. Tschermak. (Stuttgart: E. Schweizerbart'sche Verlagshandlung [E. Koch], 1883-85.)

Die Structur und Zusammensetzung der Meteoreisen erläutert durch photographische Abbildungen geätzter Schnittflächen. Von A. Brezina und E. Cohen. (Stuttgart: E. Schweizerbart'sche Verlagshandlung [E. Koch], 1886-87.)

Die Meteoritensammlung des k. k. mineralog. Hofkabinetes in Wien. Von A. Brezina. (Wien: Alfred Hölder, 1885.)

THE above three works together provide for the student a rich treasury of information relative to the characters of meteorites. The first two illustrate, by the aid of photography, the structure and composition of the more typical meteoric stones and irons respectively. The work dealincluding 25 large plates, and has been undertaken by ing with the meteoric stones is complete in three parts, Prof. Tschermak, who had charge of the Vienna Collection of Minerals from 1869 to 1877. Of that which relates to the meteoric irons only two parts have as yet appeared, but they comprise no fewer than 24 large plates:

Halothrix lumbricalis, Kutz., Symphoricoccus radians, Rke, Kjellmaniz sorifera, Rke., Asperococcus echinatus, filiformis, Rke., Ralfsia verrucosa, Aresch., R. avata, Carrn, Microspongium gelatinosum, Rke., Lptonema fasciculatum, Rke., var. uncinatum, var. majus, var. flagellare, Desmotrichum undulatum, J. Ag., D. balticum, Kutz, D. scopulorum, Rke., Scytosiphon pygmus, Rke., Ascocyclus reptans, Cr., A. ocellatus, Kütz., A. balti us, Rke, A. fœcundus, Stromf., var. seriatus, Rke, A. globoss, Rke, Ectocarpus sphæricus, Derb. et Sol, E. Stilophora, Cr., E. repens, Rke., E. ovatus, Kjellm, var. arachnoideus, Rke., Rhodochorton chantransioides, Rke., Antithamnion boreale, Gobi, var. baltum, Rke, Blastophysa rhizopus, Rke., Epicladia falls are rarely so large that the market is flooded with

it is undertaken jointly by Dr. Brezina, who succeeded tion, and by Prof. E. Cohen, of Greifswald, whose series Prof. Tschermak in the keepership of the Vienna Collecof micro-photographs of sections of terrestrial minerals and rocks is so well known.

Photography has rarely been applied to a more satis

factory purpose than the multiplication of exact represen

tations either of transparent meteoritic sections, or of etched meteoric irons as seen with the unassisted eye or when magnified by means of the microscope. Meteoritic

illustrative specimens ; and, indeed, a good collection of typical meteorites is inaccessible to most students. But, further, meteoric irons are very prone to deteriorate, through oxidation, and the perpetuation of the characters of a freshly etched face is thus especially to be desired. The excellence of the photographs is beyond all praise. The details, whether of the chondritic structure or of the Widmanstätten figures, are most beautifully shown. A brief description of the salient features of the sections is furnished with each plate.

The third work is nominally a Catalogue of the Vienna Meteorites, but, by reason of the completeness of that collection, is virtually a survey of the petrographical characters of the meteorites of all the known falls. The classification adopted is in the main that suggested by Gustav Rose in 1864, and developed by Tschermak in 1872 and 1883. The detailed description and definition of the groups is preceded by a history of the Vienna Collection, and also by a sketch of the various theories which have been proposed relative to the mode of formation of meteorites. As a result of his microscopical researches, Dr. Brezina supports the view that the structural features of meteorites are due to hurried crystallization, and not to a slow agglomeration of fragmentary matter. Dr. Brezina adds a chronological list of the meteorites preserved in the known collections, and also a lengthy index of names, synonyms, and localities. The work extends over 126 pages, and is accompanied by four plates. L. F.

Introduction to Chemical Science. By R. P. Williams A.M., and B. P. Lascelles, M.A., F.C.S. (London: Ginn and Company, 1889.)

THERE could hardly be a more concise and well-digested summary of elementary chemical principles and applica. tions than that contained in this work. It is a manual intermediate between the natural philosophy primer and the minute and detailed text-book, and fills the gap pointed out in the Report on Chemical Teaching of a British Association Committee in 1888. Hence, as an outline of chemical science to be filled up in greater detail from larger works, and as an introductory textbook, this volume will be found exceedingly useful. The experiments described are such as should be performed by everyone beginning the study of chemistry, and would also serve as an excellent introduction to a course of qualitative analysis. In addition to the treatment of metals and non-metals, the work includes chapters on organic chemistry, and others on photographic chemistry, the chemistry of rocks, and electro-chemistry. Indeed, Mr. Williams, the author of the American edition, and the reviser, Mr. Lascelles, may claim to have produced a most comprehensive little work, and one deserving considerable commendation.

The Cradle of the Aryans. By Gerald H. Rendall, M.A. (London: Macmillan and Co., 1889.)

THE question as to the primitive home of the so-called Aryan race has lately excited so much interest that many students must have wished for a short and clear account of the controversies relating to the subject. This is exactly what Prof. Rendall supplies in the present essay, the substance of which was originally communicated to the members of the Liverpool Literary and Philosophical Society. Prof. Rendall accepts Penka's theory that the Aryans were a European people who, at the close of the glacial epoch, followed the ice northwards, and settled in Scandinavia; and that Scandinavia was the centre from which, at various subsequent periods, groups of the Aryan race were dispersed. All the arguments marshalled by the German writer in favour of this hypothesis are here briefly and effectively stated. The philological part of the case is presented in a more

scholarlike spirit by Prof. Rendall than by Penka himself, whose rash philological conjectures have prevented a good many people from doing full justice to the weight of his anthropological and ethnological evidence.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE, No notice is taken of anonymous communications.]

Mr. Cope on the Causes of Variation.

MR. E. D. COPE's letter in NATURE of November 28 (p. 79) is a fair sample of his writings on biological theory, in so far as I am acquainted with them.

The tone of his letter

Mr. Cope proposes to teach Mr. Wallace and others the first principles of both logic and biology. encourages a similar frankness in reply. Mr. Cope must faults of which a critic can be guilty-namely, complete mis not take it amiss when he is charged with two of the gravest apprehension of the matter which he is attempting to criticize, and no less complete ignorance of the recognized and elementary facts of the branch of science to which that particular matter relates. I do not hesitate to assert that Mr. Cope puts forward an argument which could not possibly be enter tained by anyone who is acquainted with the most notorious and admitted facts of heredity and variation. I venture to express myself thus emphatically, because it is a matter for sincere regret that American biology should at this moment be identified with what is sometimes called "a school of philosophy" which owes its distinction to a deliberate ignoring of the writings of Mr. Darwin. By all means let us have discussion and criticism of Mr. Darwin's conclusions, but let it be understood that those who enter upon such discussion have at any rate an elementary acquaintance with the works of Mr. Darwin himself, if not with

those of Weismann and Wallace; otherwise, much time and much of your valuable space will be wasted.

That Mr. Cope has not the necessary elementary acquaintance with the admitted facts of heredity and variation will appear from what follows. The discussion in which he has intervened is one as to whether certain structural peculiarities exhibited by flat-fish are due to the transmission to their offspring of a form and position of parts acquired by muscular efforts by the ancestors of flat-fish, or whether these given structural peculiarities suddenly appeared in the ancestors of flat-fish as a "congenital variation" having no adaptive relation to any efforts or experiences of a preceding generation, and were advantageous to their possessors, so that the in tividuals thus born were favoured in the struggle for existence, survived to maturity, and transintensification as is found experimentally to be the result of mitted their peculiarity to some of their offspring with such breeding from parents both of which possess a given congenital peculiarity.

The question raised is, in short, whether in this case Lamarck s hypothesis of the transmission of acquired characters is the necessary explanation, or whether the case can be explained by the action of the known causes (not hypothetical causes) on which Mr. Darwin founded his theory of the origin of species, viz. the occurrence of congenital variations unrelated to any like variations in parents or ancestors, and the selection and intensification of such variations in subsequent breeding. There has been here no ambiguity-such as unfortunately arises sometimes when like questions are discussed-as to the sense in which the term "acquired characters" is used. It is clear enough that by the acquired characters" of a parent we do not mean characters congenital in the parent, but expressly exclude them, it is clear that we refer on the contrary (as did Lamarck) to new characters acquired by the parent as the direct consequence of the action of the environment upon the parental structure, and exhibited by that parent as definite measurable features.

[ocr errors]

Now let us consider Mr. Cope's contribution to the discussion. He accuses Mr. Wallace-who is one of those who refuse to adopt Lamarck's gratuitous hypothesis of the transmission of acquired characters-of being guilty of the sin of non-sequitur” and " "paralogism." He then proceeds to make a general statement, the truth of which neo-Darwinians (or post-Darwinians, or anti-Lamarckians), in common with all men, recognize,

although Mr. Cope offensively implies that they do not, viz. ** Selection cannot be the cause of those conditions which are prior to selection: in other words, a selection cannot explain the of anything." How can Mr. Cope presume to tell us this? Who has ignored it? when? and where? Mr. Cope does not seem to be aware of the fact that the anti-Lamarckians attach great importance to the existence of congenital variation, that Darwin himself has written at length on the subject, and that Weismann has developed a most ingenious theory as to the relatium of fertilization and its precedent phenomena to this allJaportant factor in evolution.

Mr. Cope puts aside all that has been done on that subject, or else is ignorant of it, and calmly lays down the following proposition: **If whatever is acquired by one generation were not rmitted to the next, no progress in the evolution of a character could possibly occur. Each generation would start exactly where the preceding one did." The full significance of this sentence can only be apprehended when it is understood that Mr. Cope believes that progres in the evolution of a Character does occur. The statement therefore amounts to this: (1) that whatever is acquired by one generation is transmitted to the next; and (2) that the only possible explanation of the fact that a new generation does not exactly resemble its parents at a corresponding age is that the parental generation has transmitted in ns offspring particular features acquired by it between birth and maturity.

I abt whether Mr. Cope will find any other naturalisteven the most ardent Lamarckian-to join him in these

With regard to the first, it is hardly necessary to say that it has never yet been shown experimentally that anything acquired by toe generation is transmitted to the next (putting aside parasite diseases); and as to everything ("whatever") being so trans.ted, every layman knows the contrary to be true. Culdren are not born with the acquired knowledge of their ILTERS If there were no other explanation offered of offspring varying from their parents at a like age than the hypothesis of ransmission of characters acquired by the parents on their way through life by the action of the environment, this hypothetical explanation would still be quite insufficient to account for the fact that the individuals of one brood vary enormously as compared with one another, a fact which points to the individual gerns (esg-cells and sperm-cells) as the seat of the processes which re-ult in variation, and not to the parental body which is the common carrier of them all. Assuredly these broods demonstrate that all the acquired characters are not transmitted to a theffspring.

[ocr errors]
[ocr errors]

With regard to the second proposition which Mr. Cope's statement contains, experimental fact is directly opposed to its Truth As cited by Darwin on p. 8 of the first edition of the **Ongin of Species," Geoffroy St. Hilaire showed that “unnatural treatment of the embryo causes monstrosities; and monstrosities cannot be separated by any clear line of distinction from mere variations." Mr. Darwin himself was "strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception." What he meant by being affected" is explained at greater length in the Animals and Plants under Domestication," where, in chap. xx, there is a long discussion of the causes of variability, the conclusions of which are supported by an array of observed facts which Mr. Cope cannot be permitted to ignore at his pleasure. Mr. Darwin there gives solid reasons (as was his woat) for holding that variability results from the conditions to which the parents have been exposed: change of any kind in the conditions of life, even extremely slight changes, often suffice to cause variability. But Mr. Darwin's examination of the facts did not lead him to conclude that the bodily characters acquired by the parents as the result of changes were those which manife ted themselves as variations in the off-pring. On the contrary he showed that the effect of changed conditions, of excess of nutriment, and of the crossing of distinct forms, is a **breaking down," as it were, of the hitherto fixed characters of the race, leading to the reappearance of long-lost characters and to the appearance of absolutely new characters, the new characters having no more (and perhaps not less) relation to the exciting cause which acted through the parent than has the newly-formed pattern in a kaleidoscope to the tap on the kaleidoscope tube which initiated the rea-rangement.

For Mr. Cope to complain of the methods of reasoning of

[ocr errors]

66

[ocr errors]

post-Darwinians, and at the same time without any reasoning at all to assert (as he does, not directly but by implication) that there is no such thing as congenital variation or sporting," is not quite satisfactory. When it is asserted that every feature by which a young animal differs from the structure of its parents at a corresponding age must have been acquired by one or other of the parents as actual structural features, and so transmitted as an acquired character to the offspring, the whole world of fanciers, horticulturists, farmers, and breeders, is ready with its unanimous testimony to contradict the assertion.

Let me say, in conclusion, that, as Mr. Wallace has pointed out, Mr. Darwin did not consider that variability in a state of nature was either s general or so wide in its range as later observations and reflections lead us to believe it to be. Mr. Darwin studied those causes which are found by practical gardeners and breeders to be favourable to excessive variation in animals and plants under domestication. He showed clearly that the resulting variations had no adaptive relation to the exciting causes, and were manifested in the structure at birth of a new generation, and not in that of the generation subjected to the exciting cause. No one has yet been able to give an adequate account of the frequency and range of variation of any number of animals or plants in a state of nature, because natural conditions destroy, on the average, all individuals born of two parents-except two-before maturity is reached, and those two are naturally selected in consequence of their adhesion to the specific type.

There can be no doubt from a consideration of the facts cited by Darwin that, whilst variation often is reduced to a minimum in natural conditions which remain constant, natural variations of conditions can and do occur, which excite the germ-cell and sperm-cell, or their united product, to vary as in conditions of domestication. There can be no doubt that there was in Mr. Darwin's mind the conception of a definite relation between two effects arising from changed conditions: the one being the disturbance of the equilibrium of the organism and its consequent production of variations; the other being the new requirements for survival; in fact, there seems to be, as it were, at once a new deal and new rules of the game. It is not difficult to suggest possible ways in which the changed conditions shown to be important by Darwin could act through the parental body upon the nuclear matter of egg-cell and sperm-cell, with its immensely complex and therefore unstable molecular constitution, so as to bring about variations (arbitrary, kaleidoscopic variations) in the ultimate product of the union of the remnant of the twice-divided threads of the egg-nucleus with the nuclear head of a spermatozoon. The wonder is, not that variation occurs, but that it is not excessive and monstrous in every product of fertilization. And yet Mr. Cope writes from the other side of the Atlantic to assert that there is no possible cause of departure from parental type in offspring, excepting that assumed in Lamarck's unproved, improbable speculation ! E. RAY LANKESTER. December 7.

Protective Coloration of Eggs.

SOME years ago an idea similar to that of your correspondent, Mr. Grensted (November 21, p. 53), occurred to me, as regards the protective coloration of eggs; and, curiously enough, the red-backed shrike was one of the birds whose eggs I selected for special observation. My experience has been that the ground colour of these eggs is quite arbitrary. I fear that I cannot furnish data, as I ought; but I well remember that I found in Sussex a rather abnormally pale clutch of eggs in a very dark nest; and that I regarded this, at the time, as completely doing away with my hypothesis. The evidence that I got from other, less striking instances, told about equally for and against.

Another egg, whose variations I watched pretty closely, was that of the yellowhammer. Apart from differences of marking, the ground-colour of this egg varies from pure or pinkish white, to a white rather deeply suffused with purplish-red or olivebrown. But in this case, again, the correspondence of colour between the egg and its surroundings could not be made out at all satisfactorily.

A pale and little-marked specimen of the egg of the spotted flycatcher, that was brought in to me one spring at Malvern, suggested to me that it would be worth while to observe the variations here also. But I again failed to arrive at any conclusion.

[blocks in formation]

Is the Bulk of Ocean Water a Fixed Quantity ? MR. MELLARD READE's criticism is perfectly sound. If the bulk of the ocean water on the surface of the globe has always been the same, the oceans could not at any time have been shallower than at present without a decrease in the area of the land. Consequently, the supposition that in early geological times the area of the land was larger, and the depth of the oceans less, demands the further inference that the bulk of the ocean water was less then than it is now.

When writing on the physics of the sub-oceanic crust, I saw that this was a necessary consequence of the theory, but I was not then quite prepared to discuss it. I have since had some correspondence with Prof. A. H. Green and Mr. O. Fisher on the subject, and will briefly indicate the possibilities that have occurred to us.

The first suggestion made was that, if the solar radiation was greater in Paleozoic times, there would be greater evaporation, and as the temperature of the air would also be higher, the atmosphere could hold more aqueous vapour than it does now, so that we might suppose a part of the water which is now in the ocean to have been then permanently suspended above it. Mr. Fisher, in writing to me, ad nits this possibility, and even thinks it might be feasible to estimately roughly the amount of water so suspended if the mean temperature of the ocean at any period was known. But he says:“I d› not think you could get much diminution of the oceans in this way, for, suppose the present atmosphere to consist of nothing but aqueous vapour, then it would represent a layer of water about 30 feet thick evaporated from the earth's surface. Now, it seems hardly probable that at a former time there should have been an amount of aqueous vapour in the atmosphere so great that the mass of such additional vapour should equal that of all the oxygen and nitrogen and vapour now in the atmosphere; and even if there was this amount, it would take off only about 30 feet of water from the surface of the globe," or about 37 feet from the present surface of the oceans.

If, therefore, the bulk of the wa er on and above the surface of the earth has remained the same since the time when the crust was first formed, it seems difficult to find any means of sensibly diminishing the amount of water in the oceans. But need we make this preliminary assumption, and is it not really possible that there has been an increase in the bulk of surfacewater, and not a decrease by absorption, as some theorists would have us think? May we not suppose, in fact, that water-substance has always existed in the interior of the earth, and may it not, by its constant and gradual escape, have always been adding to the bulk of the surface-waters?

This idea had occurred to Mr. Fisher so long ago as 1873, and the following passage occurs a paper then published (Trans. Camb Phil. Soc., vol. xii., Part 2 p. 431): "If such was the condition of the interior in the early stages of the cosmogony, a large portion of the oceans now above the crust may once have been beneath it"; and in the new edition of his "Physics of the Earth's Crust "he further discusses the manner in which this water-substance may be diffused through the magma of the liquid substratum beneath the crust.

As a matter of fact, it is well known that almost all volcanoes, when in eruption, emit large quantities of steam, and the presence of this steam has always been connected with the causes of volcanic activity. There are only two ways of accounting for the presence of this steam: (1) that water from the sea or from the rainfall gains access to the deep-seated foci of volcanic action; (2) that the water-substance is a primary constituent of the liquid mag na below, and that when this material is forced up to the surface, the pressure which kept the water in solution or combination is removed, and it is blown off as steam.

As regards the first possibility, there are great difficulties in the way of supposing that surface water can find its way to any region where the heat is sufficient to keep rock constantly in a liquid condition. It does seem possible that the access

of water to the interior parts of a volcano already established may sometimes cause an eruption, and, under certain circum stances, an eruption of great violence; but the descent of water through the earth's crust to depths of 20 or 30 miles 50 28 to be the initial cause of the establishment of volcanoes is not so easy to understand. The pressure of the superincumbent rocks at a depth of 2 or 3 miles must be so great that all cracks and interstitial spaces would be reduced to a minimum, and at the depth of 5 miles one would suppose that none such could exist. Several facts are known to geologists which show that all cracki diminish rapidly downwards. One such fact is that in many deep mines the throw of a fault diminishes with the depth to which it is followed. Another is the existence of such warm springs as those of Bath, the explanation of which is supposed to be that water percolating downward (say from the Mendi reaches a depth at which there is less resistance to its travelling laterally than to its further descent, and that ultimately reaching a crack or fault, it is forced up this path of least resistance l the hydrostatic pressure of the descending stream.

It is true that a residuum of the water might continue its downward journey, being, as it were, slowly sucked downward as far as the minutest interstitial spaces extended; but what would happen when it reached the lower layers of the crust? Could it possibly reach and be absorbed by or dissolved in the semi-fus! rock which must there exist? Captain C. E Dutton has well expressed this difficulty. Referring to the high temperature which must exist at a depth of 5 or 6 miles, he says:- At such a temperature the siliceous materials of which the rocks are composed are no longer hard and brittle as when they are cold, but viscous and plastic. . . . Now a crack or fissure might reach very far down into hard, cold, brittle rocks, but into soft semifused plastic rocks, never. Under a pressure of several miles of superincumbent strata, a crack, or even the minutest vesicle. would be tightly closed up as if its walls were wax or batter. more perfect packing against ingress of water could not be con ceived." 1

[ocr errors]

Even capillary action could not come into play under such

conditions as these.

Let us next consider the alternative theory suggested by Mr Fisher. He claims that geologists furnish him with a certain amount of positive evidence for the idea that water is an essential constituent of the liquid magma from which the igneous rocks have been derived. Passing over the proofs of the existence of water in the crystals of volcanic rocks and in the materials of deep-seated dykes, let us come at once to granite, a rock which can only have been formed at great depths and under great pressures, and which often forms large tracts that are supposed to have been subterranean lakes or cisterns of liquid matter in direct communication with still deeper reservoirs. Now, all granites contain crystals of quartz, and these crystals include numerous minute cavities which contain water and other liquids; and the quartz of some granites is so full of water-vesicles that Mr. Clifton Ward has said: "A thousand millions might easily be contained within a cubic inch of quartz, and sometimes the contained water must make up at least 5 per cent. of the whole volume of the containing quartz." This amount only represents the water that has been, as it were, accidentally shut up in the granite, for some was doubtless given off in the form of steam which made its way through the surrounding rocks.

It is therefore generally conceded that granite has consolidated from which all granitic intrusions have proceeded contains waterfrom a state of igneo-aqueous fusion, and that the liquid magma substance. It is therefore only a step further to assume that this water-substance is an essential constituent of the liquid sab stratum, and to suppose that it has been there since the consolidation of the earth. That there is no inherent improbability in this supposition, and that it is not inconsistent with chemical views of cosmogony, Mr. Fisher has shown at the end of has chapter on the Liquid Substratum."

I am only now concerned with it as an explanation of the secular increase in the bulk of the ocean waters which is demanded by my theory of the evolution of continents and oceans. We can prove from the geological records that volcanic action has always been in operation fro n the very earliest times in the world's history, and if it is true that such a reservoir of water-substance has always existed in the earth's interit, the continual volcanic eruptions must have constantly added water to the oceans on the earth's surface. Hence, as I stated in my "Volcanoes," by C. E. Dutton, in Ordnance Notes, Na 343, Washing ton, 1889.

« PreviousContinue »