NA TURK 



31; 



CEO-MORPHOLOC Y. 



Lithogenesis der Gegenwart. Beobachtungen iiber die 

 Bilditng der Gesteine an der heutigen Erdoberfldche. 

 Driller Theil einer Einleituiig in die Geologie als 

 hislorische Wissenschaft. By Johannes Walther. 8vo. 

 pp. viii. + 535 lojS- (Jena : G. Fischer, 1894.) 



Geotektonische Probleme. By A. Rothpletz. 8vo. pp. 

 175. 107 figures, and 10 plates of sections. (Stutt- 

 gart : E. Schweizerbart, 1894.) 



Morpiiologic der Erdoberfldche. By Dr. Albert Penck. 

 Ratzel's " Bibliothek Geographischer Handbiirher." 

 Svo. 2 vols. Vol. I. pp. .xiv. + 171. 29 figures. Vol. II. 

 pp. X. + 696. 38 figures. (Stuttgart : J. Engelmann, 

 1894.) 



RECENT discussions in England as to the relations 

 between geology and geography have only served 

 to show that these sciences are so intimately associated 

 that no satisfactory line of demarcation can be drawn 

 between the two. These three works illustrate the extent 

 to which this view has been accepted in the schools of 

 Germany and Austria, and the valuable results to both 

 sciences that follow from a due recognition of the fact. 

 The three works agree in this, though they are very 

 different in their aims and subject-matter. The first is a 

 manual on rock-formation ; thesecorid, a monograph on 

 one type of earth-movements ; and the third, a systematic 

 text-book of structural geography. One is a restatement 

 of the principles of correlation, another a protest against 

 speculation, and the other a compilation of the classifi- 

 cations of, and theories respecting, the dil't'erent geograph- 

 ical forms. They have, however, so much in common in 

 their methods, that they may be conveniently noticed 

 together. 



Prof. Walther's work goes even further. It shows not 

 only the inseparability of geology and geography, but 

 the need of a knowledge of biology for the correct appli- 

 cation of the evidence of palxontoloi.'^y to stratigraphy. 

 Since the days of William Smith, the evidence of fossils 

 has been regarded as final in both historical and strati- 

 graphical geology. It is therefore rather startling to find 

 a geologist stating that the history of the earth could 

 have been written from the structure of the rocks alone, 

 without the assistance of the organic remains within 

 them. It has been the rule, in the determination of tht; 

 age of any particular bed, to accept only the evidence 

 of the fossils as valid. So long as the method of corre- 

 lation .by the proportions of species and genera common 

 to two horizons, was confined to comparatively simple 

 areas, it gave fairly trustworthy results. But when ex- 

 tended beyond Britain and the North European plain, it 

 was the cause of serious confusion. The classification of 

 the very variable Cainozoic deposits of the Mediter- 

 ranean basin were involved by it in chaos ; it caused 

 beds in Australia to be assigned to the highest instead of 

 the lowest division of the Cainozoic, and led to lime- 

 stones in the West Indies, probably formed in part 

 within the historic period, being referred by high 

 authorities to the Miocene. Even in such a simple 



NO. 1318, VOL. 5r] 



sequence as that of England, the method led to errors, 

 as, e.g.., in the exaggeration of the gaps in the geological 

 record, such as that between the Chalk and the Lower 

 London Tertiaries. Occasionally a warning against the 

 neglect of lithology would be uttered, as by Godwin 

 Au-ten and Sorby, or an effort made to use it. But the 

 former were ignored ; and the latter were not at first 

 judicious, as in the case of the famous generalisation, 

 that we are still living in the age of the Chalk, a sugges- 

 tion about as useful as that we are still living in the 

 Silurian, because sandbanks were formed then and are 

 forming now. 



For the recognition of the necessity for the limitation 

 of palaeontology, we have in the main to thank biology. 

 Ta.xonomy— the study of distribution— has shown that 

 age is only one of many conditions that govern the 

 character of a fauna ; the depth, the composition of the 

 sea-floor, the distribution of the ocean currents, the 

 proximity of different bathymetrical zones, all exercise 

 an influence. Thus a fauna is often more allied to an 

 extinct one, than to those which are living simultaneously 

 in adjoining areas. Taxonomy has exercised its in- 

 fluence in two ways. In the first place, it has insisted on 

 the proper recognition of the self evident fact that de- 

 posits change in space as well as time : that a sandstone, 

 e.g., may change into a clay laterally as well as vertically. 

 Thus it is now recognised that the dividing line between 

 the Gault and the Upper Greensand is a varying litho- 

 logical one, and that the latter formation in one area was 

 formed at the same time as Gault was being laid down 

 in another. In the second place, it has led to the adop- 

 tion of more detailed, zonal stratigraphy, and the demon- 

 stration thereby, that adjacent beds of different composi- 

 tion, and containing different faunas, have often been 

 deposited simultaneously in stratigraphical continuity. 



These views have gradually worked their way into 

 general recognition by geologists, but Walther's is 

 probably the first text-book in which they have been 

 adequately expressed. The inconvenience in map- 

 making, and still more in map-reading, which they 

 involve, has led, perhaps, to an unconscious bias against 

 them. Hence, even when theoretically admitted, their 

 guidance has not been accepted practically. Walther's 

 " Geologie als historische Wissenschaft ' is, however, 

 saturated with the results of biological teaching, the 

 influence of which we may trace in nearly every page of 

 the " Lithogenesis." Though well skilled in palaeon- 

 tology, he does not attach an exaggerated importance to 

 the evidence of this science, but seems even to tend to 

 the other extreme : if he does not underrate its value, he 

 at least protests that it is less indispensable than has 

 been thought. In his ardour for lithology, he goes so far 

 as to say (p. 53S) that " if we had an exact phenomen- 

 ology of rocks, we could, without fossils, from the rocks 

 alone, read the history of the earth." Walther's work is 

 an effort toward such a " phenomenology," by an ex- 

 position of the lines along which it m.iy be attained. He 

 defines (p. 537) the objects of lithogeny "as the elucida- 

 tion of the development of the fossil rocks by the 

 investigation of rock-forming processes now in opera- 

 tion." He urges that rocks should be studied from the 

 same point of view as animals and plants. He thinks 

 that in comparative lithology, ontogeny should hold the 



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