7i8 



NA TURE 



L.\<nr-MhhK 17, 1923 



and overthrusting ; he deals mainly with observed 

 examples, as he regrets that tendency to consider 

 folding from general principles which has often led to 

 a geoi' 1 i.ither than a geological treatment of 



the pt Iff next deals with the behaviour of 



inder pres k ml gives an excellent account of 

 (lyiiainometamorphi.sm, mylonitisation, and the plas- 

 ticity of rocks. 



The largest part of the book consists of an account 

 of the structure of the Alps in which the author insists 

 on the " impossibility " of the overthrust theory in its 

 present dominant form. He supports the " swallowing 

 theory " which represents the crust of the eartli as being 

 under conditions analogous to those of the atmosphere. 

 In certain areas, which correspond to the anticyclones, 

 the nidvcmciit of flie material is upward, leading to 

 tlu' lormati Icanoes and the rupturing of the 



crust. In other ureas, which correspond to cyclones, 

 the crust moves downward, producing fold mountain 

 chains owing to the lateral pressure, and also wide- 

 spread metamorphism. Overthrusting inevitably takes 

 place in the subsiding area, but the thrusts have a more 

 limited horizontal extension than is claimed by the 

 upholders of the Deckentheorie , which in its extreme 

 form Dr. Heritsch describes as mere phantasy. The 

 swallowing theory is, however, not inconsistent with 

 the general contraction of the earth. It in fact renders 

 that process more probable by rejecting the immense 

 horizontal overthrusts which are too great for contrac- 

 tion alone to explain. The deformation of the earth 

 by contraction indeed supplies the power which is 

 required for regional uplifts and causes the subsidence of 

 the intensely crumpled bands which have formed the 

 fold mountain chains at different places at successive 

 periods in the earth's history. 



Dr. Heritsch's book is an able and sane statement 

 on a complex branch of geology. It should be a useful 

 corrective to the exaggerations of one school of Alpine 

 geologists. 



(2) North of the Alps lies the province of Wiirttem- 

 berg, which has been affected by some of the Alpine 

 movements but presents a marked contrast by its 

 comparatively simple though varied geology. The 

 province has played an important part in the history 

 of geology. Tubingen has been one of the great 

 geological schools of Germany, and, as Dr. Hennig 

 reminds us, both Kilima Njaro and Kenya were dis- 

 covered by men of Wiirttemberg, though they were 

 both at the time in the service of a British Missionary 

 Society. The richness of Wiirttemberg in fossils made 

 it one of the chief centres of German palaeontolog}-, and 

 the museums of Tubingen and Stuttgart are so rich in 

 types that they have attracted generations of geological 

 pilgrims. The province includes one of the most 

 NO. 2820, VOL. 112] 



typical series of Jurassic rocks, an illn 

 of pygmy volcanoes and structures tl 

 the physical and glacial geography 

 Alps. 



The comprehensive summary of the geology 

 Wiirttemberg prepared by Prof. Hennig, of Tiibingt 

 is therefore welcome, as it gives an up-to-date summa: 

 of the German Jurassic system and a guide to t! 

 localities made famous by the work of Quenstedt 

 first part has been issued, and it deals with thcoro;^ 

 and with the stratigraphy up to the end of the J un . 

 The two sections of this part which will be of wi<i< 

 interest are the account of the Trias with its ri 

 development of the Muschelkalk and of the Suabi. : 

 Jurassics, which include the rich coral reefs for whi^ 

 the locality of Natheim has been especially famous. 



The book is illustrated by two excellent colour" 

 maps, one of the orography and one of the geolog} 

 Wiirttemberg, by many clear diagrams of the pala( 

 geography and lateral variations of the rocks, and a 

 correlation of the English and German Jurasn 

 deposits. In the author's classification of valleys, p. 7 . 

 he uses the term " isoclinal valley " for those in whi' h 

 the dip is the same on both banks owing to the valley 

 having been cut in an inclined sheet of rock. This term 

 is so likely to be confused with an isoclinal in 

 the equal dip on both sides of the axis is due tu ovcr- 

 folding, that it is to be hoped that the new usage will 

 not be generally adopted ; for such valleys either the 

 terms uniclinal or homoclinal are available. 



(3) Forel's " Handbuch der Seenkunde," the stand- 

 ard text-book on the physical geography of lakes. 

 was published in 190 1, so that a new work was desirable, 

 and the previous writings of Prof. Halbfass, of Jena, 

 have shown, by his wide knowledge of the scattered 

 literature on the subject, that he is especially competent 

 for its preparation. His book is based on the principle 

 that the essential feature of a lake is its water and n< t 

 its basin. Hence a larger part of the volume is devoted 

 to the physics and chemistry of lakes than to the 

 nature of their basins. He discusses the movement- 

 of lake waters due to thermal changes, and to seichta, 

 and variations of the shore lines caused by the tilting 

 of the crust. There are short chapters on the optica) 

 and acoustical properties of lakes, including in the 

 latter the " Barisal guns," which appear, however, t 

 be due to seismic influences on delta dep)osits and to 

 have no connexion with lakes. The mirage effects in 

 some Hungarian lakes are illustrated graphically b\ .; 

 series of views taken at intervals during the day. 

 There is an especially useful summary of the chemistrv 

 of lake waters. The chapter on the biology consi.-: 

 of only two pages ; it considers the relations of some 

 animals living in deep lakes and accepts them as 



