Lartet remarks that if the Dead Sea had been situated in Europe, chemists,would no doubt have resorted to it long ago as a commercial source of bromine and of salts of potassium. As to the famous bitumen of Judea, from which the Dead Sea borrows its name of Lake Asphaltites, our author believes that its origin is connected with the existence of a system of thermal and saline springs along the axis of dislocation of the basin. Long ages after the formation of the Dead Sea, volcanic action was working at the north-eastern part, where immense quantities of basalt were poured forth, while eruptions on a smaller scale occurred also on the eastern side of the sea. The relics of this volcanic activity still linger in the form of hot, saline, and bituminous springs; and it is a significant fact that the ancient deposits of the lake are destitute of bitumen. But it is to be clearly understood that the origin of the Dead Sea is in nowise connected with such volcanic phenomena.

Some half-dozen years ago, the late Mr. David Forbes had occasion to lament the one-sidedness of the views taken by our modern school of geologists in discussing the causes which have brought about the present characters of the earth's surface. With the effects of denudation constantly before their eyes, the geologists of this country have not unnaturally been led to attach vast importance to the ceaseless working of such agents as rain and river, wind and wave. That these agents have played a most important part in sculpturing the earth's surface into its present diversity of features, no one surely would attempt to deny; but Mr. Forbes urged, with considerable show of reason, that the tendency of geological thought in this country was to dwell unduly upon these destructive forces, and consequently to overlook, if not altogether to despise, the action of subterranean powers by which new matter is constantly being forced towards the surface, and thus brought within reach of denuding forces. Unless counterbalanced by some compensating action, the solid surface of the earth would, in the long run, be destroyed by subaërial and marine denudation; the physical features of the country would be slowly effaced, and the mountains carried piece by piece into the sea. Were it not then for some internal working by which matter is forced upwards from below, it is clear that the surface of the earth must sooner or later be reduced to a level plain. Professor Geikie has estimated that, at the present rate of subaërial denudation, these islands would be levelled in about five and a half millions of years. Important, therefore, as it unquestionably is to study in detail the action of denuding agents, it is not a whit the less important to determine the operation of those internal agents which are active in the work of upheaval and reconstruction, and thus maintain a due balance between waste and renovation. In truth a geological system

ignoring volcanic phenomena would be as absurdly incomplete as a physiological system that should take no count of the function of alimentation. Every unbiased geologist will therefore seek to acquire familiarity with both classes of phenomena, and to carefully apportion to each its respective share in the economy of nature. The most thorough-going denudationist will not deny that subterranean forces are actively at work; nor can the most energetic plutonist shut his eyes to the effects of denudation. Yet Mr. Forbes was, no doubt, justified in holding that many of our English geologists have of late years shown a disposition to attach a trifle too little weight to volcanic effects. Familiar with volcanoes in many lands, and a resident for years in South America, where subterranean action is rife to an extent frequently unpleasant, Mr. Forbes was not likely to overlook the geological importance of such agents, and he consequently lost no opportunity of insisting on the magnitude of volcanic phenomena and the importance of studying igneous rocks. Now that, Mr. Forbes's voice is no longer heard, it is well that some younger man should step forward and plead on behalf of his favourite subject. We consequently need no apology for calling attention to Professor Judd's Contributions to the Study of Volcanoes."

Perhaps the most generally interesting parts of these contributions are those which relate to the origin of the Alps. The structure and formation of this noble chain of mountains, with its wide-spread system of subordinate ranges, are problems which have long exercised the ingenuity of geologists, and have served as a basis for many a warm discussion. Old-fashioned geologists were wont to regard the axis of the Alpine chain as representing a primitive formation-a portion of the solid surface of a once molten globe in its pristine condition, or a set of deposits thrown down from the turbulent waters of a still seething sea. Such notions have long since passed away, and we now know, on the contrary, that the axial portions of the mountain chain consist mainly of stratified rocks deposited during various geological periods-palæozoic, mesozoic, and tertiary-and subjected, long ages afterwards, to mechanical and chemical forces by which they have been folded and otherwise disturbed, and thus brought into their present crystalline condition. We are to conceive of the Alps as having been formed not by successive deposition of sediments upon the flanks of an ancient axis of granite, but rather by the upheaval of masses of pre-formed sedimentary matter, which became crumpled and metamorphosed by the action of masses of liquid rock forced into their midst. Those manifestations of subterranean force by which the Alps have been formed, so far from being of very ancient date,

• A second series of papers under this title communicated to the Geological Magazine (Trübner & Co.) in the course of the year 1876, and recently reprinted for private circulation.

are comparatively recent events-so recent, indeed, that the origin of the present Alps is mainly due to forces which have operated since the deposition of the clay upon which London stands.

It is certain, however, that there were volcanic outbursts along the line of the Alpine chain as far back as the Permian period. The products of these ancient eruptions are now buried beneath many thousand feet of younger sedimentary rocks, and are seen only where they have been laid bare by denuding forces, as in Southern Tyrol. There we have the well-known quartz-porphyry of Botzen, long regarded as a granite, and there too we have quartziferous lavas peculiarly interesting to the petrologist as examples of rocks which exhibit the very rare association of a plagioclastic felspar with free quartz. These Permian volcanoes afford us the earliest evidence of the existence of a line of weakness in the earth's crust along the direction of the Alpine chain. That they were active on an enormous scale is sufficiently attested by the vast thickness of the erupted material still preserved to us-a thickness of more than 9000 feet in the neighbourhood of Botzen. But this long-continued period of volcanic activity was succeeded by one of quiescence and subsidence. It was during this period of tranquillity that the vast thickness of the Alpine Trias was deposited. Thousands of feet of sandstone, limestone, and shale, were thus formed, associated, however, with volcanic material, showing that now and again the repose of the triassic seas was rudely broken, and that the old subterranean forces, though much abated, had not altogether died out. It is to this period that we must refer the eruptions which threw out the wellknown crystalline rocks of Predazzo and Monzoni. One of the most interesting of these is a characteristic rock termed Monzonite, which presents a decidedly granitic structure, but is nevertheless clearly of eruptive origin. All through the long ages during which the Upper Trias, Rhætic, Jurassic, Tithonian, Neocomian, Cretaceous, and Nummulitic formations were deposited, the Alpine area was slowly subsiding, and during this subsidence vast thicknesses of sedimentary strata were deposited. It has been shown by several distinguished American geologists that the preliminary stage in mountain-making consists of a long-continued depression of the area, and consequent accumulation of a great thickness of stratified material. Such was clearly the case in the history of the Alpine system. It was pointed out by Mr. Darwin many years ago that areas of depression are not marked by volcanic activity, and this generalisation is supported by the study of the origin of the Alps. During the Mesozoic period, when the Alpine area was subsiding, there appears to have been no volcanic outbursts, but in the Oligocene period there was a marked pause in the subsidence; elevatory forces came again into play, and, after a period of oscillation, these forces acquired the ascendency,

and in the Miocene period the elevation became decided. Regions which are subject to elevation are precisely those in which a geologist expects to see volcanic activity, and we accordingly find that the Alpine area, so long quiescent, again became the theatre of eruptive action, although, it must be admitted, not exactly along the old line of weakness. That line had indeed become strengthened by the great thickness of stratified rocks which had been deposited in the trough. Masses of rock were thus elevated in Miocene times, and by the action of subaerial forces upon these rock masses the present features of the Alps have been slowly carved out. We have been led to refer at some length to Professor Judd's papers for the sake of the remarkably clear view which they give of a rather difficult subject, and for the justice and moderation of the writer's opinions. Those who care to follow more closely the history of the formation of the Alps may be referred with confidence to a work published about a year ago by Professor Suess, of Vienna, under the title of Die Entstehung der Alpen.

As science advances, the methods of investigation become more and more delicate, and thus the crude results obtained in the early history of a science are usually displaced in its later stages by others more refined and therefore more accurate. Geological investigaYears ago a geologist

tions offer many examples of such progress. would not hesitate to name a rock after having used no aid to his natural sight beyond that of a mere hand-lens. Now-a-days, however, if he does not wish to be accused of rashness, he will need in many cases to subject his specimen to careful microscopic scrutiny. He has indeed to tediously grind down a thin section of the questionable specimen until it becomes sufficiently thin to admit of examination by transmitted light: This searching method of optical analysis was originally due to the sagacity of Mr. H. C. Sorby, and has since been actively pursued by a number of petrographers both at home and abroad. As an example of some of the most recent results of microscopic petrography, we may refer to a valuable paper by Mr. J. Arthur Phillips, read before the Geological Society on the 7th of February.

This paper dealt with the chemical and mineralogical changes' which have taken place in certain eruptive rocks in North Wales, and deserves to be selected as a typical example of the results of combining chemical with microscopical research. At Penmaenmawr, about six miles to the south-west of Conway, in Carnarvonshire, there is a great mass of felspathic rock, which has burst through the surrounding palæozoic strata, and forms a huge boss rising to a height of m or than 1500 feet above the sea-level. The toughest portions of this rock have been extensively quarried for use as a building-stone and

also as a material for paving sets. Different varieties of the stone, taken from quarries in different parts of the mountain, are found to be merely modifications of one eruptive rock. This rock appears to consist principally of a triclinic felspar and hornblende, with magnetite, and in some specimens grains of free silica in the form of quartz. It comes close to some of the so-called trachy-dolerites, but as it contains hornblende and no augite Mr. Phillips proposes to distinguish it as a trachy-diorite.

As an example of the changes which take place in crystalline rocks, and in which the natural moisture percolating through the rock, or the 'quarry water,' probably plays an important part, Mr. Phillips calls attention to the curious rock known as uralite-porphyry. Uralite was the name given many years ago by the late Gustav Rose to the peculiar crystals in certain rocks from the Ural Mountains in which hornblende appeared to take the place of augite, the crystals having in fact the form of the original augite, but the general characters of hornblende. This altered mineral occurs also in the uralite-porphyry of Predazzo in Tyrol, and in a similar rock in the Mawddach valley, near Dolgelly. Mr. Phillips has examined the Welsh rock, and finds the crystals of uralite undergoing alteration around their margins, so that the forms gradually lose their definition, and as the change progresses from without inwards the crystals become less and less distinct until they finally vanish in a cloud-like mass. The use of the microscope thus offers us an insight into the successive changes which go on within the very heart of the solid rock-changes which consist mainly in the decomposition of one component mineral and the formation of another, and which make up what we may not inaptly call the life' of the rock.

Hitherto our attention has been confined to those branches of science which deal with inorganic nature. It remains to notice the recent progress of the biological sciences.

It will be remembered that Professor Burdon-Sanderson made, a short time since, a series of observations upon the electrical condition of the leaf of Dionaea muscipula, the Venus's fly-trap. He found that, as in the muscles of animals, an electrical current exists in the leaf in its unexcited state, and that, during excitation, the current is reduced in intensity or undergoes a negative variation. The results of an investigation of a similar nature have just been published by Mr. Yule, of Magdalen College, Oxford, who has demonstrated the existence of like conditions in the fruit of Momordica elaterium, a plant of the cucumber family. The fruit in question is gourd-like, about two inches in length, and, when ripe, separates from

Journal of Anatomy and Physiology, vol. xi. part 2, January 1877.