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Printing Department, Cairo, 1905; for the Ministry of Finance). The dark outer film is similar to that well recognised as a characteristic of stones in deserts. The desert-film has been examined separately, and Mr. Lucas agrees with Walther that "the colour is much the darker the more the silica content of the rock." The depth of colour is dependent upon the amount of black oxide of manganese in the film, and this is conditioned first by the manganese content of the rock, and secondly by the opportunities presented for the manganese salts to be brought to the surface and oxidised." "A hot climate and a small rainfall are necessary to the formation and preservation of the film." In regard to the river-film, it is noted that certain incised stones at the First Cataract are equally black on their surface and in the hollows of the inscriptions. Silica is one of the minor constituents of the riverfilm, but is absent from the desert-film. Mr. Lucas, after discussing previous literature and his own analyses, conIcludes that the river-film arises from material in the rocks themselves, as in the case of the analogous desert-film. Dr. W. F. Hume contributes a description of the micro

scopic characters of the rocks examined, with the general

result that no connection can be established between the surface-film and any special decomposition in the outer layers.

THE June number of the National Geographic Magazine contains an account of a visit to Vesuvius after the eruption of April 8. The account is illustrated by a number

FIG. 1.-The new cone of Vesuvius from the road to the observatory, covered with white volcanic ash. From the National Geographic Magazine.

of reproductions from photographs, of which we reproduce one showing the aspect of the cone after the eruption. The scoring of the slope of the cone is due to slipping of the loose ashes, not to stream action.

THE current number of the Home Counties Magazine contains an interesting article on old pewter by Mr. H. M. Cooke. In a broad sense pewter is composed of tin alloyed in varying quantities with antimony and copper; lead, bismuth, and zinc are sometimes also employed. The variety and constant change of colour are due to the difference of alloys and to atmospheric influence. The colour is in some measure dependent on the surface being good. As a domestic article, pewter succeeded wood, and was used almost universally until earthenware became cheap. It did not come into general domestic use until the seventeenth century. On account of its fusibility

pewter was used by goldsmiths to take castings of certain articles. Benvenuto Cellini is said to have used it for this purpose in connection with his work. It appears from Mr. Cooke's article that dealers nowadays, to enhance the value of their wares, often point to the small marks in shields of a lion rampant or a leopard's head crowned, and describe articles bearing these as "silver pewter." But such marks indicate no special value in the metal, and except for the infinitesimal quantity that there may be in the lead employed, it is safe to assume that old pewter contains no silver.

In a paper on the rapid measurement of geodesical bases published in part i. of the Bulletin of the French Physical Society, Dr. C. E. Guillaume gives details of the construction and use of the standards and measuring wires referred to in his article on invar (NATURE, vol. lxxi., p. 138). An account is given, in particular, of the rapid, direct measurement of base lines by means of stretched wires of invariable length. This process is extremely rapid as compared with older methods; in good country, ten or twelve men can bimetallic scale fifty men are required, and the distance measure up 5 to 6 kilometres per day, whereas with a covered per day does not exceed 400 metres. Formerly the number of bases directly measured was kept as small as possible, nearly all the values being obtained by triangulation. The use of these measuring wires of invariable length affords a means of controlling the older data, and will change the character of future surveys by increasing

the number of direct data at the expense of those obtained by triangulation.

THE third volume of the contributions from the Jefferson Physical Laboratory of Harvard University for the year 1905 has been received. The previous volumes were described at some length in NATURE for March 1 last (vol. Ixxiii., p. 427). The results of the investigations published in the present volume were obtained largely by the aid of the Thomas Jefferson Coolidge fund for original research. Nine of the twelve papers have already appeared in the Proceedings of the American Academy, and most of the contributions have been dealt with already in notes published in these columns.

THE Electrician Printing and Publishing Company, Ltd., is issuing a new series of Electrician primers at 3d. each, post free. A complete list of the primers will be sent on application. From an examination of specimens dealing with thermopiles, Röntgen rays and radiography, influence machines, the induction coil, the magnetic properties of iron and electrical units, it is clear that the series will prove of service to technical students.

THE édition de luxe of the Great Eastern Railway Company's handbook, "Summer Holidays," by Mr. Percy Lindley, is provided with an excellent series of facsimiles of water-colour drawings of places of interest in the eastern counties. In addition to the illustrations in colour, the pen and ink drawings, the letterpress, the list of golf links, and other information provided, combine to make the publi cation a useful holiday guide.

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OUR ASTRONOMICAL COLUMN. REDISCOVERY OF FINLAY'S COMET (1906d).-A telegram from the Kiel Centralstelle announces the rediscovery of Finlay's comet by Herr Kopf on July 16. The position of the comet at 13h. 14.4m. (Königstuhl M.T.) on that date was

R.A.=23h. 38.3m., dec. = 14° 3' S.
The object is stated to be a bright one.
an extract from the approximate ephemeris
Herr Schulhof in No. 4100 of the
Nachrichten:-

1906

July 16

18

20

12h. M.T. Paris.

a (true) h.

m.

23 44

21 57

O II

0 25

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9'4478 9:4376 9'4299 A comparison of the observed and computed places on July 16 will give an approximate value for the corrections to be applied to the ephemeris positions. When rediscovered, the comet was about one degree north of Aquarii; at present (July 19) it is presumably about five degrees north of 2 Ceti, and is travelling in a northeasterly direction, so that it now rises above the southeast horizon at about 11.30 p.m.

THE ORBIT OF CASTOR.-An interesting paper on the quadruple system of Castor, by Dr. H. D. Curtis, appears in No. 5, vol. xxiii., of the Astrophysical Journal.

The discussion is based on the results obtained from a number of spectrograms, of each of the two double systems, taken with the Mills spectrograph at the Lick Observatory. For the fainter component, a,, of the visual system, the final elements deduced give the period as 2.928285 days, the eccentricity as 0.01 0.0066, and the velocity of the system as -0.98 +0.15 km. The comparison of these elements with the observational results shows a satisfactory agreement. Reducing the observational results for the brighter component, a,, Dr. Curtis obtained a final set of elements which give the period as 9.218826 days, the eccentricity as 0-5033±0.0112, and the velocity of the system as +6.2010.17 km.

Combining these results with those obtained for the visual system, it should become possible to obtain values for the parallax, masses, and other physical constants of this remarkable quadruple system, but the visual results, as shown in a table given by Dr. Curtis, are as yet so indeterminate that any values so obtained could not be looked upon as being in any way final. The relative

velocity of the two components as derived from Dr. Curtis's discussion is 7.14±0.23 km., and, taking Prof. Doberck's period of 347 years for the visual system, this would indicate a parallax of o".05. On a similar assumption the semi-major axes of the two systems are as follow:

α Geminorum, a = 1,435.000 km.

a = 1,667,000..

Although these results are mere hypotheses, they give some idea of the magnitude of each system, and show that they are probably of about the same dimensions.

THE SANITARY CONGRESS AT BRISTOL

THE twenty-third Congress of the Royal Sanitary Institute was held at Bristol during the week ending July 14. Sir Edward Fry presided. The proceedings of the congress comprised the usual general meetings; meetings in three sections, (1) sanitary science and preventive medicine, (2) engineering and architecture, (3) physics, chemistry, and biology; and meetings of conferences of various classes of persons interested in sanitary science. This year there were conferences of municipal representatives, under the presidency of Councillor Colston Wintle, chairman of the health committee of the City of Bristol, who took a prominent part in the proceedings of the congress; of medical officers of health, under Dr. D. S. Davies, medical officer of health, Bristol; of engineers and surveyors to county and other sanitary authorities, under Mr. H. Percy Boulnois, of the Local Government Board; of veterinary inspectors, under Mr. Frank Leigh; of sanitary inspectors, under Mr. A. E. Hudson, chief sanitary inspector, Cheltenham; of women on hygiene, under Miss Mary Clifford, in the absence of the Duchess of Beaufort; and also a conference on the hygiene of school life, under the presidency of the Bishop of Hereford.

In the presidential address to the congress on Monday, July 9, Sir Edward Fry dealt clearly and concisely with the general history of sanitary works and the regulation of public health. After pointing out the increase of duties and responsibilities which had devolved upon the heads of modern households and upon local authorities in consequence of the recent developments of sanitary science, he referred in turn to the sanitary ordinances of the Greeks, the Jews, and the Romans up to the disappearance of all thought of sanitary science in the ruin of the Western Empire. Finally, he referred to the legislation on the subject in Great Britain since the middle of last century.

ment.

Sir W. J. Collins, president of Section I., sanitary science and preventive medicine, was detained in London by urgent parliamentary duties, and the address was read by Dr. Shingleton Smith. It protested against the too exclusive consideration of bacteriology, and appealed for greater attention to be paid to the soil in which bacteria are implanted, and upon which they depend for their developIn Section II., engineering and architecture, the president, Mr. Edwin T. Hall, referred to a number of points in which the architect could assist the promotion of sanitation by the design of buildings. Dr. W. N. Shaw, president of Section III., physics, chemistry, and biology, took for his subject climate and health. After referring to the work of Sir Arthur Mitchell, Dr. Buchan, and Dr. Longstaff, he indicated the climatological material available for the study of questions upon the relation of health to climate, and discussed the methods of using it. In the course of the address he showed a meteorological section of the British Isles from north to south, Sumburgh Head to Hastings, and another from west to east, Valencia to Margate. He also exhibited some interesting diagrams of the average diurnal variation of relative humidity for certain selected months at four observatories in the United

Kingdom, and some autographic records of the same element at Cambridge, showing remarkable fluctuations of humidity within the period of twenty-four hours.

The subjects of the addresses at the various conferences and of the papers and discussions were for the most part of a technical character. Questions concerning milk supply and its regulation were raised in Section I. by Dr. J. Fortescue-Brickdale and by Mrs. C. Hamer Jackson, at the conference of medical officers of health by Prof. H. PLANETS AND PLANETARY OBSERVATIONS.-In the first of Kenwood, and at the conference of veterinary inspectors a series of articles on "Planets and Planetary Observ- by Dr. W. G. Savage and by Mr. J. S. Lloyd. The quesation" which he is contributing to the Observatory, Mr. tion of dust, particularly of motor dust, also came up in Denning discusses the general problems to be attacked various forms. In the conference of engineers it was raised and also the instrumental equipment necessary for the work. by a paper by Mr. A. P. I. Cotterell, and in Section III. After discussing the relative merits of refractors and re- the influence of dust on health was a subject of discussion flectors, he points out that no amateur observer should be opened by Dr. P. Boobbyer. Of the suggestions made for discouraged because he possesses only a relatively small dealing with the question, some of them could only be instrument, and states that none of the largest telescopes, called fantastic. The discussion of various aspects of the yet employed in this branch of astronomy shows anything bacterial treatment of sewage also found a place in several beyond what is readily distinguishable in an 8-inch glass. | sections or conferences. The necessity for the extension of

employment of women as health visitors or in other ways in connection with the carrying out of provisions for public health also appeared on more than one occasion.

Subjects to be treated from the more specially scientific standpoint fall, as a rule, to Section I., sanitary science and preventive medicine, or to Section III., physics, chemistry, and biology. In the former, Fleet-Surgeon BassettSmith suggested various ways in which disease might be disseminated in a paper on present knowledge of the etiology of Mediterranean fever, with special reference to the Royal Navy. The other papers were by Dr. R. S. Marsden, on scarlatina and certain other diseases in relation to temperature and rainfall; by Dr. J. Fletcher, on post-scarlatina diphtheria and its prevention; and by Dr. F. T. Bond, on some points of interest in the treatment of outbreaks of diphtheria. In Section III., besides the discussion on the influence of dust, may be mentioned a paper by Prof. M. Travers, F.R.S., on the absorption of gases in solids, which showed how, following the analogy of the absorption of carbonic anhydride by carbon, the absorption of water vapour by wool and by cotton varied with the pressure of the vapour up to saturation point, and also how the absorption of water vapour by cotton at the same pressure diminished with increase of temperature.

Mr. J. H. Johnston described some experiments upon the determination of the amount of organic colloids in sewage and their partial removal by surface action. Mr. J. W. Lovibond sought for a more precise chemical definition of "pure beer," and indicated the use of his tintometer to identify the quality of beers. Dr. Rideal described the effect of copper sulphate in preventing the growth of algae in water supplies, and proposed the use of electrolytic chlorine for the purpose. The other papers were of a technical character.

In an evening lecture Prof. Lloyd Morgan set forth very clearly the distinction to be drawn between the deterioration of the individuals composing a race and the degeneration of the stock, and dealt with the bearing of the theory of evolution upon the question of degeneration. A popular evening lecture was also given by Baillie Anderson, of Glasgow, on the wastage of human life.

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Ample provision was made for the entertainment of those attending the congress by visits to works and institutions in the neighbourhood, as well as by garden-parties or excursions to the numerous places of interest in the district. The excellence of the arrangements and the smoothness of the working were effective testimony to the admirable organisation of the congress as carried out by a local committee with Councillor Colston Wintle as chairman and Mr. T. J. Moss-Flower as secretary, in conjunction with the officers of the Sanitary Institute, of whom Colonel Lane Notter is chairman of council, Mr. W. Whittaker, F.R.S., chairman of the congress committee, and Mr. E. WhiteWallis secretary,

MIGRATIONS INTO NEARER AND FURTHER INDIA.'

IT..

the

was philologists who first borrowed "Dravidian" from Sanskrit and applied it to a wellknown family of languages, mostly spoken in southern India, but of which an interesting member, Brâhûî, is found far to the north-west, in Baluchistan. In the hills of Central India, to the north of the main Dravidian group, there is another and totally distinct family of languages which philologists call "Mundâ. "

name

type, but possess that of the Iranians. At any rate, if we put the Brâhûîs out of consideration for the present, it is better to name the ethnic type "Mundâ-Dravidian," i.e. the type common to the people known as Mundâs and to the people known as "South-Indian Dravidians." The type is almost certainly a mixed one. Judging from the fact that all Mundâs possess it, and that it is not possessed by all Dravidians (witness the Brâhûîs), the probability is that the Mundâ-Dravidian ethnic type belongs mainly to the Mundâs, and has been acquired through intermarriage by Dravidians originally endowed with a less persistent

It happens that the speakers of the south-Indian Dravidian languages and the speakers of Mundâ languages possess a common ethnic type--nose thick and broad, low facial angle, thick lips, wide, fleshy face, low stature, figure squat and sturdy, skin dark, and so on. This ethnic type ethnologists have called " Dravidian," an unfortunate piece of nomenclature, for (1) if language can ever be taken as a criterion of race, speakers of Mundâ languages are certainly different in racial origin from the speakers of Dravidian, and (2) some speakers of Dravidian languages, the Brahuis, do not possess the so-called Dravidian ethnic 1 Extension of part of a paper on "The Languages of India and the Linguistic Survey." read before the Society of Arts on March 15 by Dr. G. A. Grierson.

type.

When the Aryans entered India they found it inhabited by people of the Mundâ-Dravidian type. The Aryans were the more highly civilised, but as they migrated further and further into the country they intermarried with the people, and themselves commenced to acquire their physical characteristics while they retained their own language and customs, which they in turn imposed upon the MundâDravidas with whom they came in contact. We see traces of the same interchange occurring even at the present day between the Dravidians and the Mundâs. The Nahâls of the Mahâdêo Hills were once a Mundâ tribe. They came into contact with the relatively more civilised Dravidians, and adopted a mixed speech in which Dravidian predominated. Nowadays this tribe is coming under Aryan influence, and is adopting an Aryan language.

It is impossible to say whether the Mundâs or the Dravidians, or both, were aborigines of India or not. Assuming that the Dravidians were immigrants, the probability is that they entered the country from the south, and not from the north-west, as was maintained by Caldwell and others. Relationship has been alleged, with some appearance of truth, between the Dravidian languages and those of New Guinea and Australia. This subject has not yet been thoroughly gone into, and is at present under examination, but the above seems to be the conclusion which will most probably be reached.

As for the Mundâs, if they were immigrants, they must certainly have entered India proper from the north-east. Pater Schmidt, of Vienna, who attacked the question from without, and the Linguistic Survey of India, which has approached it from within, have arrived at the same result. There was once a race spread widely over Further India of which we find remains amongst the forest tribes of Malacca, in Pegu and Indo-China, and along the Mé-kong and Middle Salwin. The languages which they speak are members of what is known as the Môn-Khmêr family. Forms of speech closely connected with Môn-Khmêr are Nicobarese, Khasi (spoken in the central hills of Assam), and the various Mundâ tongues of India proper. That there is an ultimate connection between these widely separated languages must now be taken as firmly established by the latest researches of comparative philology. The matter admits of no further doubt. But this is not the limit of the discoveries. The languages of the Himalaya are, it is well known, TibetoBurman in character. Nevertheless, there are dialects spoken on the southern slope of these mountains, from Kanâwar in the Punjab almost to Darjeeling, which have a basis similar to this old Mundâ-Nicobar-Môn-KhmêrKhasi language, that has been, so to speak, overwhelmed, but not entirely hidden, by a layer of Tibeto-Burman. Then, on the other side, Pater Schmidt has shown an intimate connection between Môn-Khmêr and the languages of the south-eastern Pacific, so that there is evidence to show the existence in very early times of a people and a group of speeches extending from the Punjab right across northern India and Assam down to the extreme south of Further India and Indo-China, and thence across Indonesia, Melanesia, and Polynesia up to Easter Island, which is not so very far from the coast of South America.

In India, Nearer and Further, the fate of these speeches has been the same. In Nearer India the Mundâ languages, which were certainly once spoken in the northern plains, have been driven to the hills by Dravidians or Aryans. In Assam and Burmah the Khasis and Môn-Khmêrs have been either driven to the hills, where they survive as islands in a sea of alien tongues, or else to the coast of Pegu by the Tibeto-Burmans, and in Indo-China the Môn-Khmêrs have again been driven to the sea-board by the Tais.

The earliest seat of the Tibeto-Burmans seems to have been the head-waters of the Yang-tse-kiang. From here they migrated in successive waves along the valleys of the great rivers of eastern India, the Salwîn, the Irrawaddy, the Chindwin, and the Brahmaputra. The first three led them to Burmah, which they conquered, and where they founded a comparatively stable kingdom. Down the Brahmaputra they entered Assam, peopling the river valleys and the mountains in successive waves, failing only to occupy the Khasi Hills. Some of those who had entered Burmah settled in the Chin Hills, and, finding no room for expansion, were forced into becoming a backwash to the north, entering Assam from the south-tribe after tribe, in raid after raid-until the migration was stopped by the strong arm of British authority. Other Tibeto-Burmans went up the Brahmaputra into Tibet, which they peopled, getting as far west as Baltistan and Ladakh, and also occupying the Himalaya between Tibet and India proper. It was here that they found and partly gave their speech to the Mundâ-Môn-Khmêr tribes already mentioned.

The most recent Indo-Chinese immigration was that of the Tais. They first appear in history in Yunnan, and thence they began to occupy Upper Burmah some two thousand years ago. A great wave of immigration occurred in the sixth century A.D. Not only did they effectively conquer Upper Burmah, but they invaded Assam. They peopled the Shan States, and in the fourteenth century established themselves in the delta of the Mé-nam, driving the Môn-Khmêrs before them so as to form a Tai wedge between those of Tenasserim and those of Cambodia. This was the foundation of the Tai (or Thai) kingdom of Siam. At the present day the Tais are represented in British India by the Shans, the Khamtis, and other tribes of north Burmah and Assam.

A few words may be devoted to the latest great migration into India proper, that of the Aryans from the north-west. We cannot tell when this commenced. All that we can say is that parts of their earliest literary record, the Vêda, which was composed in the Punjab, have been considered by competent scholars to date from so far back as B.C. 2000, while others date them a thousand years later. The main line of approach was over the most western passes of the Hindu Kush, and along the valley of the Kabul River into the Punjab. Thence they spread over northern India. The entry into the Punjab was a very gradual one, extending over centuries. When the latest comers arrived they found that the language and the customs of their earliest predecessors had developed to such an extent that the former was unintelligible, and the latter were unsympathetic to them. This is reflected in the condition of the Aryan languages of India from the earliest times to the present day. There have always been two sharply differentiated groups of Indo-Aryan languages, one representing the speech of the earliest invaders, and the other that of the latest, while between the two there is a band of intermediate forms of speech which can be referred to the dialects spoken by those who were neither first nor last.

RESEARCH In terrestrIAL MAGNETISMA

THE Department of Research in Terrestrial Magnetism of the Carnegie Institution, if we may judge from its report for 1905, does not intend to let the grass grow under its feet. The work it has on hand at present comprises, inter alia, an examination, partly theoretical, by | Dr. Bauer into the secular variation of terrestrial magnetism, a discussion of magnetic disturbances observed during the eruption of Mont Pelée, a general study of the laws of the diurnal variation, a special investigation into magnetic storms, and a discussion of magnetic observations made during the eclipse of the sun on August 30, 1905.

Some Aryan hordes entered the western Punjab from the Pamirs directly to the north. Most of these settled en route in the country round Gilgit, Kashmir, Chitral, and in Kâfiristân. Here the inhospitable character of the mountains in which they took up their abode, and their own savage nature, hindered communication with their cousins in the plains, and their customs and language developed on independent lines. The latter presents extremely archaic features. Words which were used three thousand years ago in India proper, and which have since fallen into disuse in that country, have been preserved by it almost letter for letter. These Aryans from the Pamirs have lately been, identified with the Pisachas or σε Ωμοφάγοι,” who in later years became the subject of legend, and were looked upon, in the time of Sanskrit literature, as a race of demons.

In some researches the cooperation of eminent foreigners has been secured. The investigation into magnetic storms, for example, is being prosecuted under the direc tion of Dr. Ad. Schmidt, of Potsdam. The scheme, however, which figures most largely on the programme for the immediate future is a magnetic survey of the North Pacific Ocean. Arrangements have been made for observations in countries adjacent to it, e.g. China, and a wooden sailing vessel, the brig Galilee, has been specially adapted for work at sea. The brig, of which a general idea will be

FIG. 1.-The Galile.

obtained from the picture here reproduced, is of about 600 tons, and carries a crew of eleven in addition to magnetic observers. The bridge shown between the masts is intended to supply a specially favourable site for magnetic observations. The vessel has already made preliminary trips which are considered satisfactory.

The survey of the Pacific is primarily intended to furnish data for researches in which Dr. Bauer is interested, but the results should also be of immediate practical use in the improvement of charts. In addition to terrestrial magnetism, the department is providing for work in atmospheric electricity, and cooperation is intended with the new solar observatory of the Carnegie Institution, near Los Angeles, in studying the correlation between solar pheno mena and terrestrial magnetism. With the financial support which the department enjoys, it may look forward to an important sphere of usefulness, especially if it concentrates its efforts, and prefers substantiality to rapidity of achievement.

There are other institutions in America, e.g. the Coast

1 Report of Department of Research in Terrestrial Magnetism, by L. A Bauer, Director. Extracted from the Fourth Year-book of the Carnegie Institution of Washington. (Washington, D.C., 1906.)

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REPORT UPON THE CALIFORNIAN

EARTHQUAKE OF APRIL 18.

A PRELIMINARY report of the commission appointed

by the Governor of California on April 21 to obtain information concerning the earthquake of April 18 has reached us. The commission includes Prof. A. C. Lawson, State University of California, chairman; Prof. G. K. Gilbert, U.S. Geological Survey; Prof. Fielding Reid, Johns Hopkins University; Prof. J. C. Branner, Stanford University; Profs. A. O. Leuschner and George Davidson, State University; Prof. C. Burkhalter, Chabot Observatory; and Prof. W. W. Campbell, director of the Lick Observ

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The committee on coseismals, being concerned with the records of times at which the earthquake was felt, had to depend largely upon correspondence for information, and for times automatically registered the committee is indebted to seismologists in many countries. Numerous other observations were supplied by officers in the various public services. The committee on isoseismals has also received assistance from many sources.

Subjoined is a summary of the chief results obtained up to the present.

One of the remarkable features of the Coast Ranges of California is a line of peculiar geomorphic expression which extends obliquely across the entire width of the mountainous belt from Mendocino County to Riverside County. The peculiarity of the surface features along this line lies in the fact that they are not due, as nearly all the other features of the mountains are, to atmospheric and stream erosion of the uplifted mass which constitutes the mountains, but have been formed by a dislocation of the earth's crust, or rather a series of such dislocations, in time past, with a differential movement of the parts on either side of the plane of rupture. In general, this line follows a system of long, narrow valleys, or where it passes through wide valleys it lies close to the base of the confining hills, and these have a very straight trend; in some places, however, it passes over mountain ridges, usually, at the divide separating the ends of two valleys; it even in some cases goes over a spur or shoulder of a mountain. Along this line are very commonly found abrupt changes in the normal slope of the valley sides giving rise to what are technically scarps. These scarps have the appearance of low, precipitous walls, which have been usually softened and rounded somewhat by the action of the weather. Small basins or ponds, many having no outlet, and some containing saline water, are of fairly frequent occurrence, and they usually lie at the base of the small scarps. Trough-like depressions also occur, bounded on both sides by scarps. These troughs and basins can only be explained as due to an actual subsidence of the ground, to an uplift of the ground on one side or the other, or on both sides. The scarps similarly can only be ascribed to a

known as

rupture of the earth with a relative vertical displacement along the rupture plane. Frequently small knolls or sharp little ridges are found to characterise this line, and these are bounded on one side by a softened scarp and separated from the normal slope of the valley side by a line of depression. In many cases these features have been so modified and toned down by atmospheric attack that only the expert eye can recognise their abnormal character; but where their line traverses the more desert parts of the coast range, as, for example, in the Carissa Plains, they are well known to the people of the country, and the aggregate of the features is commonly referred to as the earthquake crack."

This line, which can be traced from Point Arena to Mount Pinos, in Ventura County, has a length of 375 miles, is remarkably straight, and cuts obliquely across the entire breadth of the Coast Ranges. To the south of

Mount Pinos the line either bends to the eastward, follow

ing the general curvature of the ranges, or is paralleled by a similar line offset from it en echelon; for similar features are reported at the Tejon Pass, and traceable thence, though less continuously, across the Mojave Desert to Cajon Pass and beyond this to San Jacinto and the southeast border of the Colorado Desert. The probability is that there are two such lines, and that the main line traced from Point Arena to Mount Pinos is continued with the same general straight trend past San Fernando and along the base of the remarkably even fault scarp at the foot of which lies Lake Elsinore. But, leaving the southern extension of the line out of consideration as somewhat debatable, we have a very remarkable physiographic line extending from Point Arena to Mount Pinos which affords every evidence of having been in past time a rift, or line of dislocation, of the earth's crust, and of recurrent differential movement along the plane of rupture. The movements which have taken place along this line extend far back into the Quaternary period, as indicated by the major, well-degraded fault scarps and their associated valleys; but they have also occurred in quite recent times, as is indicated by the minor and still undegraded scarps. Probably every movement on this line produced an earthquake, the severity of which was proportionate to the amount of

movement.

The cause of these movements in general terms is that stresses are generated in the earth's crust which accumulate until they exceed the strength of the rocks composing the crust, and they find a relief in a sudden rupture. This establishes the plane of dislocation in the first instance, and in future movements the stresses have only to accumulate to the point of overcoming the friction on that plane and any cementation that may have been effected in the intervals between movements.

The earthquake of April 18 was due to one of these movements. The extent of the rift upon which the movement of that date took place is at the time of writing not fully known. It is, however, known from direct field observations that it extends certainly from the mouth of Alder Creek, near Point Arena, to the vicinity of San Juan, in San Benito County, a distance of about 185 miles. The destruction at Petrolia and Ferndale, in Humboldt County, indicates that the movement on the rift extended at least as far as Cape Mendocino, though whether the rift lies inland or off-shore remains as yet a matter of inquiry. Adding the inferred extension of the movement to its observed extent gives us a total length of about 300 miles. The general trend of this line is about N. 35° W., but in Sonoma and Mendocino counties it appears to have a slight concavity to the north-east, and if this curvature be maintained in its path beneath the waters of the Pacific it would pass very close to, and possibly inside of, Capes Gordo and Mendocino. Along the 185 miles of this rift where movement has actually been observed, the displacement has been chiefly horizontal on a nearly vertical plane, and the country to the south-west of the rift has moved north-westerly relatively to the country on the next se of the rift. By this it is not intended to imply north-east side was passive and the south-w in the movement. Most probably the r opposite directions. The evidence of the the differential movement along the

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