314 



NATURE 



[January 31, 189- 



same place as it does in comparative morphology. This 1 

 lithology he divides into three sections, equivalent to 

 those adopted in biology. Thus, he says that the study 

 of rock structure answers to comparative anatomy, the 

 development of rocks now in process of formation 

 to embryology, and petrography and stratigraphy to 

 paleontology. Throughout the book he introduces 

 biological terms and phylogenetic trees to emphasise 

 his views. For example, he classifies rocks as homo- 

 logous and analogous ; as the former, he includes all 

 those which are formed in the same " Facies-bezirke,'' 

 and as the latter, those which are formed under 

 different geographical climates. And climate, in the sense j 

 of this later-day lithology, is " the sum of all the meteor- 

 ological and oceanographic conditions, including organic 

 and inorganic processes,' which affect the formation of a j 

 rock. The use, however, of these terms often appears of 

 doubtful value ; thus, when he states that the lavas of an 

 oceanic island are only homologous with those of a 

 continent, we doubt whether we are in any way better 

 for the information. 



The work is divided into three parts, entitled, 

 respectively, " General Lithogeny,' " the existing Facies- 

 bezirke," and '• the bases of Comparative Litho- 

 logy." The first of these occupies fourteen chapters : 

 it begins with an account of the destruction, deposition, 

 and alteration of rocks. The destructive processes he 

 divides into four classes : weathering, chemical, physical, 

 and organic ; ablation, both of ice and rock surfaces ; 

 transport ; and corrasion. The last he restricts to the 

 comparatively insignificant polishing action of loose 

 material carried about by the wind, rivers, ice, or sea. 

 -According to Walther's scheme, denudation results from 

 ablation, transport, and corrasion ; he attributes it to 

 four agencies, viz. the wind acting by " deflation," run- 

 ning water by " erosion," glacier ice by " exaration," and 

 the sea by " abrasion." The second part of the book is 

 the longest ; each chapter is devoted to the description of 

 a group of deposits, which he says are " homologous," as 

 they are formed in the same " facies-bezirke" or 

 geographical zone. Thus, on the continents there is the 

 zone of the Polar Regions, with moraines, humus, ochre, 

 &c. ; the temperate zone, with its black earth, loess, &c.; 

 the desert girdle, with its sand and salt deserts, and 

 dried-up lake-basins ; and the tropical zone, with its 

 laterite and cotton soil,&c. Other groups of homologous 

 rocks are the products of continental volcanoes, shore 

 deposits apd those of open seas, of oceanic abysses ; 

 coral reefb, and volcanic islands. Very obvious objections 

 to this classification could be easily raised, and it cer- 

 tainly could not be recommended for the purposes of 

 ordinary teaching ; but as long as it is used only to illus- 

 trate the association of deposits, formed under any par- 

 ticular set of geographical conditions, it is extremely 

 useful. The different subjects treated in the work are, 

 moreover, brought well up to date. Thus, e.g., in the 

 account of the supposed iron-secreting organism Gail- 

 lonella, the latest botanical researches of Molisch are 

 summarised, and its character left more doubtful than 

 ever. The chapter on coral-reefs is especially well 

 done. The sketch of the life of a reef (pp. 915 y-7), 

 which he calls the "richest of bionomic assemblages," 

 IS the best we know. The definition (p. 909) of a coral 

 NO. I 3 18, VOL. 51] 



reef as being essentially formed of branching corals, 

 with calcareous sediment filling the interspaces, ex- 

 presses a truth which is often overlooked. Even this is 

 enlarged on another page, where it is stated that geolog- 

 ically a reef must be regarded as including not only the 

 calcareous sediment on the surface, but that which is 

 formed around it, to the depth of as much as 3000 

 metres. He illustrates the slopes around coral islands 

 by the numerical method, due to Dietrich, which brings 

 out clearly the differences between such atolls as those 

 of the Bahamas and Keeling Island. The mean 

 figures which he gives do not, however, teach much. 

 It is interesting, therefore, considering that the coral 

 island question is handled with full knowledge of all the 

 latest information, and that the author's own investiga- 

 tions took place upon a region to which Darwin's theory 

 was never intended to apply, to notice that he accepts 

 that theory as substantially correct. It is surprising, 

 considering the accuracy of the rest of the chapter, that 

 a recent photograph of a Pectinia quadraia is again 

 quoted (p. 899) as a Manicina arcolata. 



The third section of the work is that which enunciates 

 the general conclusions. It contains short chapters on 

 the correlation of facies, the equivalence of rocks, the 

 changes in the facies of deposits, and the lithological 

 significance of organisms. This part of the book is, how- 

 ever, the least satisfactory ; perhaps because most useful 

 originality had been expected in it. Variations from the 

 ordinary method of treatment and overstrained analogies 

 had been passed in the hope that they would be turned 

 to some account. This part of the book is, however, so 

 general in its treatment, that the conclusions are rather 

 indefinite. Nevertheless, the work is throughout so 

 novel in treatment, so up to date in its information, that 

 this cannot seriously impair its value. 



Rothpletz's " Geotektonische Probleme " is a very 

 different work from either of the others. Its title is a 

 little misleading ; one might expect from it an account 

 of earth-movements in general, and a discussion of the 

 theories of earth-structure by which these may be ex- 

 plained. One is, therefore, a little startled at finding 

 that it commences with a protest against theories, and a 

 warning against the danger of ideas creeping into general 

 acceptance, under cover of a convenient term. Me points 

 out, for example, that Suess'sterm of " horst " for a moun- 

 tain mass formed of one block of material, is so useful 

 in descriptive geology, that it has been widely adopted. 

 Rothpletz fears, therefore, that Suess's theory of the 

 origin of " horsts," and its corollary that horizontal beds 

 are never uplifted, may be unconsciously accepted. 

 Similarly he foresees that, by the adoption of other con- 

 venient terms, the whole heresy of " Suessism " may 

 gradually work its way into a position of influence it 

 would never attain by its merits. The perils to geological 

 progress threatened by this insidious " hypothesis building 

 phantasy," as Rothpletz calls it, he thinks can only be 

 averted by the critic, whose duty it is to bring all 

 hypotheses to the test of facts. And the author sets him- 

 self to pcrlorm this task. His volume is devoted to the 

 class o( earthniovements known as " overlhrusts'' 

 When cases of the inversion and repetition of strata were 

 first noticed, they were regarded as due to the folding of 

 the beds. During recent years, many of these have been 



