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Die Theorieen über die Enstehung der Koralleninseln und Korallenriffe und ihre Bedeutung für geophysische Fragen. Von Dr. R. LANGENBECK. Leipzig: Verlag von Wilhelm Engelmann, 1890. Pp. 190.

This work may be described as an elaborate exposition in defence of Mr. Darwin's theory of coral reefs by a German scientist, and as such it will receive serious attention in this country. For the thoroughness of research displayed in its pages, and for the able handling of a large mass of conflicting data, Dr. Langenbeck's contribution stands amongst the foremost of the recent additions to the literature of the subject. He is able to point to the recent support given by the two eminent geologists, Professors Suess and Neumayr, to the theory of Darwin and Dana; yet his widening the field of the controversy, by including a discussion as to whether the land or the sea is the unstable element, can scarcely be said to strengthen Darwin's original view. In fact, Dr. Langenbeck considers it as immaterial to the theory of subsidence whether we conceive a sinking of the land or a swelling of the sea; and, whilst reviewing the subject, he leaves this important matter an open question until the closing chapter, when he discusses the theory of Suess of an alternate heaping-up of the oceanic waters at the Equator and the Poles, and decides in favour of the instability of the earth's crust,

The author commences his criticisms of the views of Semper, Agassiz, Murray, and the other opponents of the theory of subsidence, by ruling that the very regions that raised many of these hostile witnesses (the Philippine Islands, the West Indies, the Floridas, the Solomon Group, etc.) present very different conditions for coral-reef formation than are found in the areas to which Darwin and Dana applied their explanation. This is virtually an admission that the theory of subsidence is no longer what it was intended to be and universally accepted as, viz., a general explanation of the origin of coral reefs. It has, in fact, only a partial connection with the subject as a whole; and if the labours of Agassiz, Murray, and others had only resulted in bringing about the recognition of this fact, they would have been amply rewarded. The investigation of those complex conditions under which a coral reef is built, of the difficult biological, chemical, and physical questions involved, could scarcely be expected in a work like that of Mr. Darwin, which dealt only with the subject from a single standpoint. From this circumstance, therefore, Dr. Langenbeck's criticisms of the occasional discordant opinions of the opponents of Darwin lose much of their force. We are at present only beginning to have an insight into the nature of the problem to be solved; and if Dr. Langenbeck and the other supporters of the theory of subsidence claim certain features in the structure of oceanic atolls as supporting their views, it is not improbable but that they may be in a measure right. But the admission that a subsidence of the earth's crust might explain certain features in oceanic atolls by no means implies that this is an important factor in the matter. Certainly, it has little to do with the general subject of reef-formation.

However, dismissing the more controversial part of this work, it will be regarded for its treatment of the purely geological aspect of the question, and for its excellent account of the present distribution of coral reefs, which is, in fact, one of the most extensive compilations of the kind yet published, as well as for the masterly yet courteous handling of a somewhat thorny subject, as conveying much instruction to both sides in this discussion.

By Professor

Die Denudation in der Wüste und ihre geologische Bedeutung.
JOHANNES WALTHER. Leipzig S. Hirzel, 1891. Pp. 570.

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The author, who has travelled much in the Egyptian deserts, and whose work on the coral-reefs of the Red Sea is well known, gives in this volume an admirable account of the manner in which desert regions are denuded. He shows that the Egyptian deserts, although they are practically rainless, have yet suffered extensive erosion. This destructive work he attributes chiefly to the sun and wind-a view which, of course, is not novel, but the precise modus operandi of these two agents is explained and illustrated by Professor Walther in such a manner as to throw much additional light upon a subject which most geologists, perhaps, have been under the impression was already sufficiently understood. The author points out that the alternate heating by day and cooling by night to which rocks in the desert are exposed, result in wholesale desquamation and disintegration of the surfaces, which greatly facilitates the chemical action of water. But as dry winds and sunheat soon suck up any rain or dew, chemical action plays a very subordinate part in the demolition of the rocks. Indeed, it is only in places where rock-surfaces are sheltered from the direct action of the wind and sun that traces of that action become apparent. Weathering of this kind, which is so common in regions like our own, has in a practically rainless desert a very limited development. In like manner the disintegrating action of plants is necessarily at a minimum. The rock-materials, broken up by the action of insolation, are borne along by the wind and used as a sand-blast to attack and erode the rocks against which it sweeps. This has hitherto been supposed to be the chief work performed by the wind, but, according to the author, it is as a transporting agent that wind plays the most important part in the denudation of a desert. The disintegration of rocks in a desert is confined to their exposed surfaces, and were "deflation" or the transporting action of the wind to cease, denudation would quickly come to an end. But in a region destitute of vegetation the wind tends to carry all loose material away from the scene of its origin to the borders of the desert. This action goes on without ceasing, day and night, and during all seasons, and the result is seen in the deeply eroded rocks—enormous masses of which have been gradually disintegrated and carried away. In the rocky deserts evidence of denudation is conspicuous on every hand, but the products of the denudation have been removed. Here are great walls of granite rising to heights of 6000 feet, but showing no slopes of débris below, as would infallibly be present under temperate climatic conditions. There, again, are deeply excavated Wâdis, containing no beds of gravel and grit, such as would not fail to show themselves had the depressions in question been formed by water action. Everywhere deep cave-like hollows have been excavated in the rocks, and yet these hold no loose materials, but are swept bare. Again, over the plains mushroom-shaped rocks and hills are of common occurrence. All these appearances are due to deflation. Insolation, weathering, and the sandblast are merely the servants of deflation. They are the silent miners, the author remarks, who hammer and drill the rocks day and night to prepare loose materials which are swept away by the winds. One of the most interesting parts of this monograph is that which deals with the configuration of the surface in desert regions. The writer shows that the forms assumed by the rocks is due partly to their petrological character. Thus, granite hills, under the action of the wind, are readily distinguished from hills of sandstone; but the forms that result from such action differ essentially from those that are the result of denudation in other lands. Thus we see in desert regions projecting rock-masses that resemble the ice-worn hillocks of glaciated tracts, but on closer inspection we find no rough lee-side.

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Granite hills, again, frequently show jagged sharply-notched summits and crests, strongly resembling the characteristic features of the Dolomite mountains of South Tyrol. Another characteristic work of deflation is the production of plains of denudation-features which are of common occurrence in the desert. The products of denudation come in for considerable discussion by the author. He shows that these are of various kinds. In the rocky deserts quantities of rock-débris are met with. These mark the first stage in the desert-formation. Locally they attain considerable development, the blocks and stones being partly angular, partly rounded. But away from the rocky wastes the "deflation plains "" are encountered, where the superficial accumulations are composed of gravel, sand, or loam. In places the gravel is rounded, in other places it is sharply angular, the rounding being due to the action of the sand-blast, while the angular character results from the splitting of the stones by insolation. The sand is made up chiefly of the quartz; the loam or clay of the decomposed felspar of disintegrated crystalline rocks. The intimate structure of the accumulations in the sand- and claydeserts is not easily studied, but it is obvious those deposits must in many respects resemble formations which are common enough all the world over. Thus, a section through such desert-accumulations, were they to become solidified, would exhibit beds of sandstone with interstratified layers of clay and gravel; the sandstone would show much diagonal-bedding, while foot-prints, rain-pits, fossil wood, etc., would frequently appear. Have we any evidence, then, the author asks, of fossil deserts? Do any of the formations of this and other countries (which have usually been attributed to the action of water) really owe their origin to wind action? The study of this extremely interesting work would certainly lead us to conclude that "insolation" and "deflation " may have played a much more important rôle in the past than has hitherto been believed. But geologists have already recognised the wind-blown origin of certain sandstones, such as the Bunter Sandstones of England, and certain of the Carboniferous Sandstones of Scotland appear likewise to be Æolian formations, so that wind as a prominent geological agent of change has not been ignored. From Professor Walther stay-at-home geologists, however, will get many hints and much assistance in trying to understand the full meaning of wind-denudation. We confess to some doubt as to whether all the rock-erosion described by the author is attributable wholly to wind and its allies. There seems to be strong evidence to show that the now desert regions of North Africa were formerly well watered. The Wâdis (however much they may have been subsequently modified by deflation) have the systematic arrangement of valleys which have been excavated by rivers, and the beds of some of those in the Libyan Desert are described as being paved with water-worn shingle and gravel. Were Central Europe to become a desiccated region, the present features, which are due to the action of rain, rivers, frost, etc., would in time be greatly modified by wind-but the configuration assumed by the land would not be the result of wind-denudation alone. The hills, bared of vegetation, and their rocks exposed to surface disintegration, might well be worked over by the winds in such a way as gradually to assume the aspect which is peculiar to the hills of a desert region. One is inclined to suspect, therefore, that the wind-sculptured hills described by Professor Walther existed as hills before the desiccation of North Africa had commenced. But, however that may be, the author has put it beyond doubt that erosion on a large scale has been effected by deflation alone, and we can strongly recommend his work to the attention of all who are interested in the subject of the origin of the earth's surface features, and of the various modes in which sedimentary accumulations have been elaborated. The work, we may add, is illustrated by eight plates, which show the action of insolation, weathering, the sand-blast,

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deflation, etc., and the character of the desert sands. There are also numerous illustrations scattered through the text.

Historic Towns. Edited by EDWARD A. FREEMAN, D.C.L., and Rev. WILLIAM HUNT, M.A. New York, by THEODORE ROOSEVELT; and Boston, by HENRY CABOT LODGE. New York and London: Longmans, Green, and Co., 1891. Pp. 232, 3 Maps and Index; and 242, 2 Maps and Index. Price 3s. 6d. These two volumes, although both welcome additions to the series, differ considerably in their method. Mr. Roosevelt has written about New York city only, while Mr. Lodge has gone far outside Boston, and produced what is as much a history of New England as of its metropolis. Consequently the former's book is much the more satisfactory. He is master of a clear, vigorous style, and he has used skill and judgment in his selection of materials. His work sketches rapidly, but with sufficient fulness for all the purposes of the general reader, the history of the great city that has now long since stretched its arms beyond Manhattan Island, and far up past the Harlem River. Here we see its rise carefully and intelligently traced, from the little port where privateersmen and pirate captains swaggered in their chains of gold and jewelled daggers, through the years when it was an important political centre, the home of the Federalist party, to its present prosperity as one of the world's great trading-towns. But Mr. Roosevelt probably regards New York as of most interest as an experiment in democratic government; and, strong as his hopes are for the future, he is anything but blind to the blunders and corruption that have disgraced the city's past history. We cannot share all his confidence when he says, "If the citizens can be thoroughly waked up, and a plain, naked issue of right and wrong presented to them, they can always be trusted." Surely this would appear to be contradicted by the history of the past year or two? Some exception might also be taken to his remarks on Fulton, and his praise of the Seventh New York Regiment as "by all odds the best regiment in the United States Militia" is quaintly extravagant. However, all this is not geography, and we may gladly overlook such trifles, and thank Mr. Roosevelt for a bright, clear, useful history of his city. The same, with more modified enthusiasm, may be said of Mr. Lodge's book. There seems to be too much of the colony, and space is wasted that might have been filled with more interesting matter about the city. Even the part it has played as a literary centre is scarcely spoken about. But, for all that, Mr. Lodge has made an interesting volume; it is not all about Boston, but it will well repay perusal.

The Normans, told chiefly in relation to their Conquest of England. By SARAH ORNE JEWETT. London: T. Fisher Unwin, 1891. Pp. xv+373.

("Story of the Nations" Series.)

Price 5s.

The present volume is to be judged, not as a scientific, but rather as a popular, work. The chief faults to be found with it affect presumably the editor of the series, though we are not quite sure of this, because the writer is aware of them, and sees fit to make a sort of apology for them. Bearing in mind the other books of the series that have already appeared, one would have expected a story of the Northmen or Vikings, which might or might not have included a story of the Normans, correctly so called-i.e. the Scandinavians who colonised Normandy, and sent forth the conquerors of England and Sicily. But the present book is neither the one nor the other; it is, on the contrary, a piecemeal production, embracing a piece of the history of the Northmen or Vikings, a piece-a large piece-of the history of the

Normans, and a piece of the history of England. The title best answering to the contents of the book would be "History of the Norman Conquest of England"; out of the total of 370 pages 200 are taken up with a description of the life and deeds of William the Conqueror. A true history of the Normans ought to include an account of the doings of the De Hautevilles in Italy and Sicily. In this book this portion of Norman history is dismissed in less than twenty pages. A history of the Vikings ought to embrace an account of the doings of the sea-kings in Shetland, Orkney, Faerö, Iceland, Ireland, England, Flanders, France, Bjarmeland, Novgorod, and away down to Miklagaard (Byzantium). All this is done in fifty pages, and the greater part of it is not alluded to at all. Then again, does not the history of William 1. and William II. (with whose death, curiously enough, the book concludes) belong to the "story of England"? Altogether, we must confess ourselves at a loss to understand what is the nation whose story it is professed to tell in this volume.

Taking what we have got, however, we gladly acknowledge that the author has produced a readable book. She has honestly endeavoured to depict the life, and customs, and sentiments of the age she deals with, and writes with a good knowledge of the facts, and in a very agreeable style, which in many passages becomes even imaginative or picturesque, as the case may be. The best parts of her work are perhaps the account of William's invasion; and the account of the feudal chivalry, its customs, manners, and beliefs, is interesting. She of course follows Mr. Freeman; but it is a pity she did not discard his pedantic "Eadward" and "Aelfred." Why did she not write also "Hrolf," "Harald," "Baudewyn," and so forth, especially as she prefers Cnut to Canute? There are numerous illustrations and a couple of maps.

The Voyages and Adventures of Ferdinand Mendez Pinto, the Portuguese. Done into English by HENRY COGAN. With Introduction by ARMINIUS VAMBÈRY. "The Adventure Series." London T. Fisher Unwin, 1891. Pp. xxxii +464. Price 5s.

When the adventures of Mendez Pinto first became known to English readers— now well-nigh two hundred and thirty years ago—they were not accepted as authentic, and the oft-repeated sneers at "tales of a traveller" met the publication almost universally. But inquiry and scientific analysis of the contents of the volume showed, in time, that what the traveller had to tell was substantially fact and worthy of sufficient credence to make his collections useful to the geographer and the student of manners and customs of a past age singular for the stirring history of its adventurous voyages. Pinto, it cannot be denied, frequently exaggerated and as frequently fell into mistakes; but, looking to the stormy nature of his life and the opportunities he had for observation, the work is one of undoubted value and entertainment. This is an abridged edition, and the editor has done the work of curtailment in a singularly satisfactory manner-the omissions generally being confined to the long, dry, and florid orations of questionable authenticity with which the original Portuguese and English editions were overloaded. Probably no other narrative places before us in the same vivid light the hardships, the perils, and the wild life of the mariner of the sixteenth century, as well as the fanatic conduct of Christian and Turk and the merciless reprisals they made one upon the other. In a purely geographical sense this volume is the best of the "Adventure Series" yet issued.

The illustrations accompanying this edition number six, and are taken from The Voyage of John Huyghen Van Linschoten to the East Indies (1586-92),

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