Page:Popular Science Monthly Volume 5.djvu/392

378 the true significance of these sand and gravel deposits was not before seen. Mr. Geikie has pointed out that the deposits occurred during an intermission of the Great Ice Age, when the ice melted and disappeared from the land, which became clothed, instead, with trees and plants, and peopled with animal forms. In the course of ages the arctic conditions returned and covered the land again with ice. He has also pointed out that this alternation of temperate and arctic climate has certainly occurred more than once, probably several times. Mr. Geikie's inference becomes still stronger when viewed in the light of Mr. Croll's new theory of a periodic change of climate resulting from the precession of the equinoxes and the increase of eccentricity in the earth's orbit. We have no room for an explanation of Mr. Croll's theory, but must content ourselves with referring the reader to Mr. Geikie's book, where he will find it lucidly stated.

Now, these facts have a very important bearing on the history of man. The remains that we have gathered of primitive man are divided into paleolithic, or those belonging to the Old Stone Period, and neolithic, or these belonging to the New Stone Period. The paleolithic remains are characterized by the rudest kind of stone implements, implements merely chipped out of stone, without any attempt at finish, and from first to last there is no evidence of improvement in their make. The neolithic implements, on the other hand, are much better made at the starting-point, and they gradually improve, until they give place to implements of bronze. Again, the paleolithic remains are accompanied with the remains of mammalia, such as the mammoth, etc., which are now wholly or locally extinct, while the mammalian remains found with those of neolithic man are of existing species. Lastly, the paleolithic remains are found in the deposits of sand and gravel we have described as imbedded within the till, while the neolithic remains are found only in the upper drift. Thus in one and the same way the existence of man is shown to extend to inter-glacial, probably to preglacial times, and the meaning of the apparent gap in his history between the paleolithic and neolithic ages is explained. The paleolithic, or interglacial, perhaps pre-glacial man, was driven from the country, or destroyed by the change from a mild to an arctic climate; and, when the arctic conditions passed away for the last time, his place was filled by the neolithic, or post-glacial man, from more southern latitudes. We have indicated in a necessarily general manner the central idea of Mr. Geikie's book; it contains a great deal of very interesting information of a subordinate character, which will amply repay perusal.

we were called upon to state the object for which this book was written, we should say that it was to display what the author evidently fancies to be a very wide and accurate knowledge of science. With all the flourish and clatter of a Don Quixote charging the windmill, he impinges the mighty lance of querulousness against the feeble form of gravitation, utterly annihilating that venerable body. The atomic theory in chemistry, and the Fayian and Franklinian theories in electricity share the same fate, as do many kindred absurdities long fostered by the ignorance of man. And, as if those blows did not inflict punishment enough on the physicists, they are utterly crushed by the entirely new and astonishing revelation that final causes are unknowable. The present volume is on physics, and the most appalling fact that it contains is the announcement that it is to be followed by similar volumes on metaphysics, ethics, etc.

recently noticed this important and valuable work, and we now again refer to it simply to inform such of our readers as may be interested, that the publishers have issued a special American edition (in one volume) at a reduced price, which will make it more accessible to that large class of students to whom it makes a serious difference whether the price of a book is nine dollars or five dollars.