24 MARCH 1894, Page 16

BOOKS.

THE STORY OF OUR PLANET.* PROFESSOR BONNEY has long ago secured himself a position of authority among geologists, not only by continuous worit in the field and by his theoretical writings, but by the graphic and limpid style in which his teaching is embodied. We had every right, therefore, to expect from him a book in which the latest and most authoritative views on the subject would be presented in an attractive form, and this promise is amply fulfilled in the work before us. Its style is excellent, clear, and terse, without the use of technical and unusual phraseology. The illustrations are not only aptly chosen, but what is a great advantage, they are new and not hackneyed ; some of them are in colours, and are master- pieces of chromo-lithography, others are beautifully en- graved. There can be little doubt that any one who is not a professed geologist, who wishes to consult a work on geology which shall not only be up to date, but shall also be readable and interesting, as well as accurate and logical, will do well to turn to this volume. In the space at our command, we can only point out those features of the book which differentiate it from others. First, a word or two in respect of matters in which we are disposed to be critical. The author tries to excuse the paucity of his references on the ground that Science is a great Mart, where those who meet must be content to borrow or lend without being exacting about acknowledgment. We take a different view, and hold that, except in merely popular literature, men should not use the observations or the researches of others, especially of young and comparatively unknown men, without adequate references. The references in the present volume, which professes to be a book for serious readers, are scanty and scattered, and chiefly to easily accessible and in many cases popular manuals, and to well- known names. There are very few references to the vast litera- ture in which the detailed work of the science is recorded, and especially very few to German, French, and American memoirs and papers, or to the larger works of the great foreign geologists. Perhaps if these had been more consulted,_ the author would hardly have proclaimed himself so uncom- promising a champion of uniformity, as that gospel was taught by Hutton and by Lyell. Certainly there are signs on all sides that men are largely reverting to the more sober views of Murchison. Suess and Lapparent, Nikitin and Prestwich, are notable names among those whose lanterns are turned in another direction.

Professor Bonney, again, has engaged in many polemics, in which an incisive pen has done him yeoman's service. It is natural, therefore, to find that on some of the most debated issues in geology, he takes a strong side, and writes with the barbed pen of one directly interested, rather than in the impersonal fashion of a judge. This adds piquancy to his pages, but it will not conciliate those whose outlook is a very different one. The work is not meant to be a pronounce- ment of new views. Nor is it addressed directly to students or to those who have to teach. Its purpose is to lay before educated people the best ascertained results of geology in logical and plain language. When he is at his beat, and where the reader will find the most profit, is in those parts of the work devoted to the fields where Dr. Bonney is a specialist, and has done original work, namely, when he is dealing with the action of glaciers, with the structure of igneous rocks, and the theoretical issues they involve. To use his own words, his task has been "to give some

• The Story of Our Planet. By Professor T. G. Bonney, D.Sc., LL.D., F.R.S. With Coloured Plates and Maps, and about 150 Illustrations. London: 0843801.1 and Co.

idea of the processes by which the earth has been moulded and shaped into the stage on which all the tragedy and all the comedy of human life have been enacted." After a few elementary paragraphs on the world as a unit among the celestial spheres, he treats, in three short chapters, of the physiography of the land, the air, and the sea respectively. He describes the varying contour of mountain and valley, and the general structure and arrangement of rocks beneath the surface ; analyses the causes of winds and hurricanes, their effects and their distribution ; and discusses the seas, their currents and tides, the contours of their beds, and, finally, the conditions under which those frozen seas, the glaciers, move. In a striking sentence he shows, what few people realise, that the depressions of the seas below are far greater and more important than the elevations of the land above the water-line. Turning next to the dynamical forces and the various tools which have sculptured and moulded the earth, he divides them under two heads,—namely, external and internal. Among the former, he names the work of the atmosphere, of rain and rivers and of ice (both as sculptors and transporters), and of the sea ; and, lastly, of the various living organisms which have built up such large masses of rock, and which he calls the proletariats of Nature, some of them animals, others vegetables. Here Dr. Bonney's book has a formidable rival in the immortal work of Lyell. Yet it sustains the comparison. The graphic and illuminating illustrations of his argument, drawn from his own wide experience, are at once fresh and and inspiring, and the phrases are all his own ; and when we say this, we mean they are incisive and picturesque. Thus, speaking of the hard flints so often left in situ when their matrix has been washed away, he says : " Nature's teeth are sharp and strong, but these are awkward morsels, so she has eaten the peach and left the stone lying about." In regard to the erosive action of rivers having carved out the majority of valleys, creeks, and canons, Professor Bonney is a champion of the older conclusions of Lyell, upon which Time's erosive teeth are making considerable inroads, and will make more. Here, again, the sober teaching of Murchison is likely presently to prevail. In regard to the action of ice, his well-known views are marked by more sobriety. He cham- pions the main conclusion of Principal Forbes, that ice moves as a plastic body. He urges strongly that it abrades but does not excavate, and contests the theory of Ramsay and others that the greater part of mountain lakes were, or could have been, excavated by ice. He similarly questions the validity of the appeal continually being made to that hypo- thetical child of the imagination, a ground moraine, apropos of which—as tested by the Alpine glaciers—he says " Here and there a boulder may be seen on its subglacial journey ; the surface of rock or of ice may be smeared with mud, but the debris, so far as is known, simply travels and does not accumulate ; " and he speaks of this theory as " looming large in literature, but being comparatively a dwarf in the realm of fact." He even ventures to throw doubt on the view that portentous ice-sheets once filled the North Sea and the Irish Channel. Dr. Bonney holds an even balance between the champions of the views of Darwin and Murray on the origin of coral-reefs, theories which have exercised biologists much of late. We wish we had space to quote more from the interesting chapter in which he discusses the work of the humble living architects of limestone and chalk, of coal and of turf, than its concluding sentence. In this, he says " The very dust has been once alive, and the chief ministrants to the comfort, the prosperity, and the civilisation of man have been the humbler members of that living world at the head of which he claims to stand."

Having discussed the external agencies which have shaped the earth, he next turns to the internal ones,—to those mysterious forces which are controlled by Pluto, and which rock and shake and sometimes rend the solid floor on which we live and move ; forces which work with intermittent vigour, and whose most outspoken lessons are seen in volcanoes and earthquakes. He argues forcibly that the effects we can examine support the old view of a molten condition for the interior of the earth, rather than the notion that they are the products of local chemical action. While pointing out difficulties in all the theories hitherto published, he speaks highly of that of Mr. Mellard Reade about the origin of mountain chains and of ocean depths, and urges that in some way or other they are the wrinkles and puckers in the earth's skin caused by its shrinking. Volcanoes he treats as phenomena entirely detached from these larger earth movements, and attributes them, and the geysers or hot springs with which they have so much in comb mon, to the action of steam upon the molten masses beneath. The lavas which proceed from volcanoes are connected by composition, structure, &e., with the great masses of basalt and other intrusive rocks of an older time, and which flowed out in various ways ; " sometimes pouring out through gaping cracks and fissures, and thus reaching the surface ; sometimes forcing their way under- ground between two masses of uniformly stratified rock, like a paper-knife thrust between the pages of a book, as if the upper bed had been too solid to allow further progress in that direction, and yet the pressure from below on the plastic mass had enabled it to rend the layers apart, and to lift up the overlying one." Dr. Bonney gives the weight of his great authority to the notion that igneous rocks are not the products of the local melting down of sediments, but re- present the outer part of the magma of which the earth is composed. Turning to earthquakes, " shudders of the earth's cuticle," as he calls them, which often cause great change of level and the opening of wide fissures, he argues that their cause, whatever it be, is at a depth never exceeding thirty miles, and very commonly about five miles, and that they occur chiefly where volcanoes are either active now, or have recently been so, and in mountainous districts where the mountains are geologically young. Of their probable cause, Dr. Bonney says :—" We can readily understand that in a volcanic region the earth's crust may be sometimes shaken by the subter- ranean explosion of gases, or may be rent asunder by the pressure of a mass of lava as it forces its way underground, or may tremble from the sudden subsidence of strata which have been left unsupported by the condensation of vapour." Dr. Bonney then turns to the mechanical and chemical changes which have taken place in rocks after they have been deposited. " Cleavage " he makes " the effect of the pressures set up where rocks are sharply folded." This origin of slaty structure is confirmed by every kind of evidence. In regard to faults, he says :—" As these may bring, when the displacement is con siderable, masses of rock into contact which differ very much

in hardness and durability, they may determine the direction of valleys and the trend of escarpments." As an example of the enormous shifting involved in some parts, he notes a fault in the Appalachians in America, which, " though it produces- no marked effect on the scenery, has so dislocated the rocks- that, on one side of a crack over which a man can stride, the highest of the Upper Silurian beds faces the lowest of Lower Silurian. This means a displacement of 20,000 ft." In regard to chemical changes which have occurred in rocks in situ, and which are caused principally by water, pressure, and heat, and their effects, he has some clear and instructive paragraphs, in which he shows how mud has become mica-schist, limestone has been converted into marble, and sandstone into quartzite, and lastly, how, by the filtration of hot water, veins and fissures have been filled with their mineral contents.

In that part of his work devoted to the story of past ages, namely, the various eras in geological history, Professor Bonney chiefly follows well-known guides and conventional views, and has little to say which is new. The story con- tinues to be told, however, in the same plain, clear, picturesque style and with the same sober judgment. This part of the work condenses most of the more important generalisa- tions of recent times ; but they essentially represent the

geology of twenty years ago, and their author—especially in the appendices—clings to conclusions on many points which are dissolving away and passing into oblivion.

A striking passage may be quoted from the concluding chapter as a sample of picturesque diction :-

" Nature is the schoolmistress of all living creatures, and harder than the sternest of all human pedagogues. She never spoils the child by sparing the rod, or remits the penalty for any crying. The motto so well known to the Wykehamist, seems to be writ large on the walls of her schoolhouse= Aut disco, aut discede ; manet sors tertia caedi,' which may be freely translated, Change yourself as conditions change ; begone elsewhere would you live as you did, or stay to suffer and to die.' " In conclusion, this book, while it will not for the serious student and the teacher occupy the ground of such excellent and standard works as those of Geikie, Prestwich, and Horace Woodward (each a masterpiece in its way), will do a great

service to that increasing number of educated people who wish to know the history of our planet without the trouble and harass of original investigation. If not a manual for the geological workshop, it is probably the best geological work available for the library of an educated man.