98 



NATURE 



[June 3, 1897 



idea of the change which has taken place. Some con^ 

 stituents are readily removed ; others, especially the 

 alumina, are comparatively insoluble under ordinary 

 conditions, and therefore remain behind. Thus, Columns 

 III., IV. and V. show the loss or gain of the various 

 constituents estimated on the basis of constant alumina. 

 We may remark, in passing, that alumina may be re- 

 moved under certain conditions ; as, for example, when 

 sulphuric acid is formed by the oxidation of pyrites. 

 This shows the necessity of caution in taking alumina 

 as the basis of comparison, but it does not affect the 

 present case. From Column III. we learn that 31 per 

 cent, of silica, i -3 of ferric oxide, the whole of the lime, 

 and the greater part of the magnesia and alkalies have 

 been removed. The total loss amounts to 44 per cent. 

 In this case, the breaking down of the rock has been 

 accompanied by decomposition as well as disintegration; 

 in other cases decomposition is not so prominent, and 

 the total loss is consequently much less. 



Many rocks are treated in the same way, but one other 

 illustration must suffice, and for the complete data in 

 this case we must refer the reader to the book itself. 

 In certain parts of America, and indeed in all countries 

 where limestones are extensively developed, and where 

 the residual products of decomposition are allowed to 

 accumulate for a considerable length of time, a super- 

 ficial deposit of red or brown clay is formed. In these 

 cases the author considers that silica may be assumed 

 to be constant, and taken as the basis for calculating 

 the amount of material removed. He thus arrives at the 

 conclusion that in the particular case described by him 

 97 per cent, of the original limestone has disappeared. 

 In some localities residual clays of this kind attain a 

 thickness of from 20 to 120 feet. 



Having considered in detail a number of special cases 

 in the manner above described, the author proceeds to 

 deal with the influence of joints of texture, of mineralogical 

 composition, of climate, and many other factors. All 

 these points are discussed in the light of recent know- 

 ledge, and the chapters devoted to them are full of 

 interesting and important information. Illustrative cases 

 are mostly drawn from American sources, and this gives 

 to the book a refreshing novelty, at any rate to English 

 readers, even when well-known principles are treated. 

 Especially interesting are those portions dealing with 

 climate. It is pointed out that in cold and dry climates, 

 subject to extremes of temperature, disintegration is the 

 dominant factor ; whereas in moist, warm climates 

 decomposition is very pronounced. Thus the careful 

 study of the petrographical character of sediments may 

 be expected to throw important light on the climatic 

 conditions of those regions which furnished the material. 

 This point is, of course, not new ; but its importance has 

 not been fully recognised, and it is therefore satisfactory 

 to see that the author gives it a prominent place. 



The concluding part of the book deals with the super- 

 ficial deposits for which the term regolith is proposed. 

 Under this term is included not only the soil, subsoil and 

 residual products of decornposition, but also the alluvial, 

 leolian, and glacial deposits. We are by no means con- 

 vinced that the author was well advised in departing 

 from his general and most praiseworthy determination to 

 avoid as much as possible the introduction of new terms ; 

 NO. 1440, VOL. 56] 



but the point is, after all, of comparatively slight 

 importance. If the term supplies a want, it will come 

 into general use ; if not, it will die out. 



The petrographical characters and conditions of forma- 

 tion of the various deposits classed as the regolith are 

 described, and we are glad to see that special attention 

 is paid to the reolian formations, as these often receive 

 scant courtesy at the hands of geologists. Loess, how- 

 ever, is discussed under alluvial deposits, although it is 

 ascribed in part to the action of the wind. Surely there 

 can be no doubt that typical loess is of aeolian origin ; and 

 if, in America or elsewhere, alluvial deposits have been 

 included under this term, this should be recognised as a 

 mistake, and speedily rectified. 



The work is admirably illustrated by twenty-five plates 

 and numerous figures in the text, all of which have been 

 produced in the manner so highly appreciated by those 

 who are acquainted with American geological literature. 



MECHANISM AND BIOLOG Y. 

 Zeit- und Streitfragen der Biologie. Heft 2. Mechanik 

 und Biologie. Von Prof. Dr. Oscar Hertwig. Pp. iv -|- 

 211. (Jena: Gustav Fischer, 1897.) 



FROM the title of this work one might have expected 

 a critical examination of the vahdity of the general 

 principles of modern biology, more particularly of modern 

 physiology ; and such a criticism, from the pen of Dr. 

 Oscar Hertwig, would have been welcome and instruc- 

 tive. It is with a feeling of disappointment that one 

 finds that his criticism is almost entirely. confined to a com- 

 paratively limited aspect of the question, and is, in fact, a 

 polemical treatise directed especially against the preten- 

 sions and conclusions of Wilhelm Roux and his school. 

 It is, no doubt, a simpler task to refute the theories of 

 Roux ; but if Dr. Oscar Hertwig is victorious in this par- 

 ticular argument, it must not be supposed that he has 

 weakened, or that he has even attempted to weaken, the 

 conviction held by the majority of biologists, that the 

 explanation of vital processes is to be sought for on 

 "mechanical" principles. There is, however, a consider, 

 able amount of obscurity attached to this word 

 " mechanical " as applied to biological phenomena, and 

 many pages of this book are devoted to pointing out the 

 errors into which we may be led if we use the word in a 

 loose and general sense, or if we confuse its philosophical 

 with its physical meaning. In its widest sense a 

 mechanism is a system of objects, which in place and 

 time stand in a necessary relation to one another. Hence, 

 when we describe the attitude of contemporary science 

 as mechanical, we do but assert that science is con- 

 vinced that the operations of nature are subject to the 

 control of universal law. Of this the biological are as 

 much convinced as the abiological sciences ; yet this con- 

 viction does not necessarily lead to the conclusion that 

 the methodsof the abiological are in all respects applic- 

 able to the biological sciences. To discuss this question 

 is to discuss the philosophical basis not only of biology, 

 but of all the sciences. As a contribution to the discus- 

 sion. Dr. Hertwig gives us copious quotations from 

 Spinoza, Kant, Lotze and other philosophers, skilfully 

 selecting such passages from these thinkers as best serve 

 his immediate purpose of refuting Roux. His readers 



