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Gems and Precious Stones can be purchased either mounted or unmounted. BRYCE-WRIGHT, Mineralogist and Expert in Gems and Precious Stones. 204, REGENT STREET, LONDON, W. THURSDAY, NOVEMBER 9, 1882 A SEARCH FOR "ATLANTIS" WITH THE MICROSCOPE THE THE revival of the idea of a former "Atlantis" has given rise in recent years to much ingenious argument. The presence of so many widely separated islands or groups of islets along the depression filled by the Atlantic Ocean has to some writers been in itself sufficient proof of a submerged continent, the islands remaining still above water as the last visible relics of the foundered land. The same conclusion has been drawn from the Atlantic soundings, which have undoubtedly shown the existence of a long ridge running down the length of the Atlantic at an average depth of some 2000 fathoms from the surface. From this ridge rise the oceanic islands of Tristan d'Acunha, Ascension, St. Paul, the Azores, and Iceland. Other writers have invoked the former presence of land over the Atlantic area, from the difficulty of otherwise accounting for the resemblance of the flora in North America and Europe during later geological times. On the other hand, it has been forcibly argued that in every case the peaks of the supposed submerged land are of volcanic origin, that not a single fragment of any truly continental rock has been detected on any of these islands, and therefore that no evidence can be adduced save of a submarine ridge on which volcanic cones have gradually been built up above the sea-level. Reasoning based on similar data furnished by the other great oceans, and also upon the evidence supplied by the stratified rocks as to the permanence of the continental areas, has led many thoughtful geologists to regard the ocean-basins as primeval depressions of the globe's surface, and consequently to reject the tempting hypothesis of a lost Atlantis. This vexed question was one on which it was hoped hat the Challenger Expedition might cast new light. The careful surveys of the ocean-floor made by that Expedition, and the attention it paid to the nature of the emergent peaks were precisely the kinds of direct obserration needed to supply facts in place of previous mere speculation. We must patiently await the completed Reports before the final answer of the Challenger observers s given. But an interesting and important instalment of evidence and argument has just been published in the orm of a "Report on the Petrology of St. Paul's Rocks," by M. Renard of Brussels, whose name is itself a uarantee for the accuracy and exhaustiveness of the memoir. Sent in to the Challenger authorities as far back s October, 1879, it is now issued as Appendix B in olume ii. of the Narrative of the Expedition. No more typically oceanic an island anywhere rises out of the deep than the lonely wave-washed rocks of St. Paul Lying nearly on the equator and between 500 and oo miles to the east of the South American coast, these ocks consist of four principal rugged horse-shoe-shaped masses not a quarter of a mile in their greatest length, and mounting into five peaks, the highest of which does tot exceed 60 feet in height. Their bare rough summits ave a yellowish tint that deepens into black towards sealevel So utterly barren are they that not a plant of any VOL. XXVII.-No. 680 kind—not even a lowly lichen-clings to their sterile surface. Are these rocks the last enduring remnants of a continent that has otherwise disappeared, or are they portions of a volcanic mass like the other islands of the same ocean? To those who have not noted the modern progress of geological inquiry it may seem incredible that any one should propose to solve this problem with the microscope. To seek for a supposed lost continent with the help of a microscope may seem to be as sane a proceeding as to attempt to revive an extinct Ichthyosaurus with a box of lucifer matches. Yet in truth the answer to the question whether the St. Paul's rocks are portions of a once more extensive land depends upon the ascertained origin of the materials of these rocks, and this origin can only be properly inferred from the detailed structure of the materials, as revealed by the microscope. The importance of microscopic examination in geological research, so urgently pressed upon the notice of geologists for some years past, has sometimes been spoken of disparagingly as if the conclusions to which it led were uncertain and hardly worth the labour of arriving at them. We occasionally hear taunts levelled at the "waistcoat-pocket geologists," who carry home little chips of rock, slice them, look at them with their microscopes, and straightway reveal to their admiring friends the true structure and history of a whole mountain-range or region. That the sarcasm is often well-deserved must be frankly conceded. Some observers with the microscope have been so captivated by their new toy as to persuade themselves that with its aid they may dispense with the old-fashioned methods of observation in the field. But there could not be a more fatal mistake. The fundamental questions of geological structure must be determined on the ground. The microscope becomes an invaluable help in widening, and correcting the insight so obtained; but its verdict is sometimes as ambiguous as that of any oracle. In any case it must remain the servant not the master of the field-geologist. Perhaps no more suggestive example could be cited of the use of the microscopic study of rocks even in the larger questions of geological speculation than that which is presented by an examination of the material composing the islets of St. Paul. These rocks were described many years ago by Mr. Darwin as unlike anything he had ever seen elsewhere, and which he could not characterise by any name. He found veins, of what he believed to be serpentine, running through the whole mass. The observers of the Challenger Expedition looked upon the St. Paul's Rocks as composed of serpentine. But these remote islets have never until now been subjected to modern methods of petrographical investigation. M. Renard has studied them chemically and microscopically, and finds them to be composed of a granular olivine-rock, containing chromite, actinolite, and enstatite. A remarkable structure is presented in the thin sections when seen under the microscope. The large crystals or grains of olivine and enstatite are arranged with their vertical axes parallel to the lines of certain bands in which the minuter constituents are grouped, the whole aspect of the section suggesting at once a movement of the component particles in the direction of the bands. When the rock was first sliced and examined by the naturalists of the C Challenger some years ago this minute structure was looked upon as what is known to petrographers by the name of "fluxion-structure," such as may be seen in obsidian and other volcanic rocks, the ingredients of which have arranged themselves in layers or planes according to the direction in which the mass while still molten was moving. The same view was at first adopted and published by M. Renard. He now, however, expresses himself more doubtfully on the subject, and indeed is rather inclined to class the rock among the crystalline schists. Now the importance of the point in question will be at once perceived when it is stated that if St. Paul's Rocks belong to the series of schists, they must once have lain deeply buried beneath overlying masses, by the removal of which they have been revealed. They would thus go far to prove the former existence of much higher and more extensive land in that region of the Atlantic; land too, not formed of mere volcanic protrusions, but built up of solid rock-masses, such as compose the framework of the continents. If, on the other hand, the rock is volcanic, then the islets of St. Paul belong to the same order as the oceanic islands all over the globe. M. Renard reviews the arguments so cautiously that only towards the end do we discover him rather inclining to the side of the crystalline schists. With all deference to so competent an authority, however, we venture to maintain that the balance of proof is decidedly in favour of the volcanic origin of the rock. In the first place, as the distinguished Belgian petrographer himself admits, the law of analogy would lead us to expect the peridotite of St. Paul to be a volcanic protrusion. So cogent, indeed, is the argument on this head that, unless some irrefragable evidence against it is furnished by the rock itself, it must be allowed to decide the question. When the rock is studied under the microscope it presents precisely the banded fluxion-structure of true lavas, thus corroborating the inference of a volcanic origin for the mass. To say that this structure also resembles the foliation of true schists is to repeat what may be remarked of hundreds of examples of undoubtedly eruptive rocks. Unless some peculiarity can be shown to exist in the St. Paul's rock inconsistent with the idea of its being a volcanic extravasation, we are surely bound to regard it as no exception to the general rule that all oceanic islands are fundamentally of volcanic origin. M. Renard, however, fails to adduce any such peculiarity. He appears to have been led to doubt the validity of his first conclusions, and, be it also remarked, those of other observers, by finding so many published instances of peridotic rocks among the crystalline schists. A bed of peridotite among a group of schists, however, need not be of contemporaneous origin, any more than an intrusive sheet of basalt can be supposed to have been deposited at the same time and by the same processes that produced its associated sandstones and shales. Synchronism is not necessarily to be inferred from juxtaposition. We do not mean to dispute the assertion that some peridotites belong to the series of crystalline schists. But others are most assuredly eruptive rocks. It is among these that we should naturally seek for analogies with the rock of St. Paul. To sum up the reasoning we may infer that, judging from the structure of other oceanic islands, the ma terial comprising the rock of St. Paul should be of volcanic origin; this inference is confirmed by chemical and microscopical analysis, and especially by the discovery of a minute structure in the rock identical with that of many lavas, though a similar structure can be recognised in some schists; the islets of St. Paul furnish therefore no evidence of an ancient land having formerly existed in the middle of the Atlantic Ocean, on the contrary they have probably been built up on the submarine Atlantic ridge by long continued volcanic eruption like the other islands of the same Ocean. The exhaustive methods of research employed by M. Renard in the study of the rock of St. Paul furnish an excellent illustration of the great strides made in recent years by petrography. The other rocks collected by the Challenger Expedition are to be treated in the same manner, but it is understood that instead of being thrown into separate Reports the petrographical details will be interspersed through the "Narrative" at the places where the localities are described. These contributions will form not the least important parts of this great work, the advent of which has been so long and so patiently ARCH. GEIKIE waited for. THE LIFE OF CLERK MAXWELL The Life of James Clerk Maxwell, with a Selection from his Correspondence and Occasional Writings, and a Sketch of his Contributions to Science. By Lewis Campbell, M.A, LL.D., Professor of Greek in the University of St. Andrews, and William Garnett, M.A., Late Fellow of St. John's College, Cambridge, Professor of Natural Philosophy in University College, Nottingham. THIS volume will be heartily welcomed by all who knew Clerk Maxwell, and who cherish his memory, and by the still wider circle of those who derive pleasure and new vigour from the study of the lives and work of the great men that have gone before them. The work consists of three parts, a biography with selections from Maxwell's correspondence, a popular account of his scientific work, and a selection from his poetry, both juvenile and of later years, including the serio-comic verses on scientific subjects, some of which are already so well known. The biography is mainly the work of Prof. Lewis Campbell, whose schoolboy friendship and life-long intimacy with Maxwell amply qualified him for the task. As far as vicissitudes of fortune are concerned, the life of Clerk Maxwell was absolutely uneventful. Worldly struggles he had none; from the very first he was warmly, if not always quite fully, appreciated by all whose good opinion he could have valued; promotion such as he cared for came almost unsought, and scientific distinction of the honorary kind was conferred upon him unstintedly while he lived to enjoy it. But in truth all these things moved his serene spirit as little as they disturbed his outward life; the interest of his biography lies in tracing the growth of a mind which was dedicated, literally from infancy, to the pursuit of science, and which nevertheless neglected nothing becoming a man to know. For unity of aim and singleness of heart, for high-minded neglect of the worldly strife that is begotten of vanity, ambition or love of gain, for the steadfast pursuing of a path remote from the ways of ordinary men, the life of Maxwell stands in our mind associated with the lives of Gauss and Faraday. Nevertheless, without seeking to compare him with either of these great men in respect of intensity of genius, we may safely assert that he was superior to both in universality and many-sidedness. The mere objective circumstances of the career of such a man count for little, and the biographer tells his tale so far as these are concerned, with an artless grace that befits the subject. It is needless to dwell upon them here, for our readers have already been furnished with a summary of the outward events of Maxwell's life (NATURE, vol. xxi. p. 317). The interest and freshness of Prof. Campbell's story lie in the light it throws on the subjective influences that moulded the character of the gentle physicist, a character which was the most extraordinary combination, that this generation has seen, of practical wisdom, childlike faith, goodness of heart, metaphysical subtlety, and discursive oddity, with wonderful critical sagacity and penetrating scientific genius. Intellectual power, and to some extent also eccentricity, appear to have been hereditary with Maxwell, as will be seen from the racy notes at the end of the first chapter on the Clerks of Penicuik and the Maxwells of Middlebie. After the early loss of his mother, he became the constant companion and confidant of his father, who initiated him into all his economic mysteries, interested him in applied sciences of every kind, encouraged his boyish essays in physical experimenting, and anxiously patronised his earliest memoir, on Cartesian Ovals and kindred curves, read to the Royal Society of Edinburgh by Forbes when its author was a boy of fourteen. This sympathy between father and son continued unbroken to the end, and had undoubtedly the happiest effect on Maxwell's destiny. The chapters on the student life at Edinburgh and Cambridge are deeply interesting, and we earnestly commend them to the young men of our time who wish not to seem, but to be indeed, men of science. With his appointment to the chair in the Marischal College, Aberdeen, begins his career as a recognised authority in scientific matters. Henceforth the biography is mainly an account of Maxwell's contributions to the advancement of physical science; the purely personal interest revives in the sad chapter that recounts his last illness and death. Glimpses into his mental history during the later period of his life are afforded us by means of extracts from his intimate correspondence, and from essays, some read at Cambridge to a select circle of friends, others, not intended for publication even to that limited extent, but merely written as records of the author's communion with his own soul. We thus learn how the great physicist dealt with the grand problem of man's relation to that which went before, and that which shall be hereafter. It cannot but be profoundly interesting to read what was thought on such a subject by one of the greate-t scientific minds of our day. We are left in no doubt as to the solution in which Maxwell ultimately reposed, and it is instructive to note how in this respect, as in so many others, he was akin to Faraday. Some will doubtless think that needless emphasis is laid upon the exact form of the final solution, and upon the precise methods by which it was reached. It must be remembered that the difficulties of the man of action and of the scientific man or professed thinker, are widely different. The former rests naturally in the arms of precept and dogma; he is distracted merely by the choice of preceptor and authority. The thinker by profession must examine for himself; it is a necessity of his nature so to do; and his difficulties arise from having to deal with matters in which the best of his scientific methods fail. Thus it happens that the example of a scientific mind is little likely to profit the unscientific; and that one scientific mind is scarcely in such matters to be led by the experience of another. The solutions of the great problem by different minds of the highest order have, as we know, differed, in outward appearance at least, very widely. But is it well to dwell on these differences? seeing that no man of finite intellect can tell how little or how great after all the distances may be that separate the resting places in the infinite of good men and true. With regard to the selections from the correspondence it might have been better perhaps, in the interest of science, to have given more of the scientific correspondence. It must be known to many of our readers from pleasant experience that Maxwell was indefatigable in writing and answering letters on scientific subjects. His letters rarely failed to contain some sagacious criticism, some ingenious thought, or some valuable suggestion. Most possessors of such letters would we imagine be glad to put them at the disposal of a competent editor for publication, or at all events to take some steps to prevent the ultimate loss of matter so full of interest for all scientific men. Those that have read the volumes containing the correspondence of Gauss with Bessel and Schumacher will understand how instructive such collections can be. Not the least interesting parts of the biography are the chapters containing extracts from the occasional essays already referred to. Maxwell when a student at Edinburgh had attended the lectures of Hamilton, and had been greatly impressed by that distinguished philosopher and accomplished enemy of the exact sciences. Accordingly, we find that among the studies of his earlier years mental and moral science had no small share. He resolves, for instance, at one period to read Kant and to make him agree with Hamilton, and, at the same time, he criticises in a somewhat unflattering strain the flaccid morality embodied in the lectures of Christopher North. It is not surprising, therefore, that the subjects of these occasional essays are mainly metaphysical or psychological. They are mostly very discursive, and their graver meaning is often veiled in a cloud of that humorous irony which figured so much in his familiar conversation. The general tendency is, however, sufficiently plain in the essay on Psychophysik, for example, he thus delivers his opinion on the theory of " Plastidule Souls," which played so prominent a part lately in the classic duel between Virchow and Haeckel, and in sundry ultra-physical discussions nearer home : "To attribute life, sensation, and thought to objects in which these attributes are not established by sufficient evidence, is nothing more than the good old figure of personification." At the end of the same essay he thus sums up the |