i6 



NATURE 



[January 31, 1895 



to one another, and this results in the type named by 

 Suess the " Schuppen-structure." The chapter concludes 

 by a consideration of the classification of earth-move- 

 ments, and its difficulties ; that advanced by Suess, he 

 recognises as the most important, but he does not admit 

 it as at all satisfactor)-. 



This shyness of classifications is in striking contrast to 

 the attitude of the last work, in which all the types of 

 " earth-forms" are classified in a detail, and with a term- 

 inology, which seems at first needlessly elaborate. The 

 work is a systematic account of the orography or struc- 

 tural geography of the earth, and is quite unlike any 

 existing textbook. It has taken more than ten years to 

 prepare. The delay has been partly due to the enormous 

 amount of literature that has had to be considered, but 

 also to the fact that during this period two works have 

 appeared which have completely changed the whole 

 aspect of geographical science. These are Richthofen's 

 " Fiihrer fur Fiirschungsreisende," and Suess' " Antlitz 

 der Erde." The former introduced a more scientific 

 classification of " earth-forms" or geographic types, 

 while the latter has revolutionised our ideas as to how 

 those eanh-forms have been developed. One of the 

 great advantages of Prof. I'enck's work is that it is a 

 re-description of the earth's surface in the terminology 

 and in accordance with the views of these two leaders of 

 geographical thought. It is a book which it is impos- 

 sible to summarise. It is a compilation showing on 

 every page the most- detailed care and accuracy. No 

 one acquainted with Prof. Penck's previous writings will 

 be surprised at his extensive knowledge of the literature 

 of both geography and physical geology. The numerous 

 historicalsummaries that occur in it, show how thoroughly 

 the author has ransacked literature, and how well the 

 book has been brought up to date. Works published so 

 late in 1894 as that containing Heim's description of the 

 Pleistocene earth-movements in the Alps (" Die Enste- 

 hung der Alpinen Randseen "), and Giinther's memoir on 

 the influence of atmospheric pressure on isostacy, are 

 included. It is only natural that English literature is 

 not so thoroughly done as the German, but important 

 omissions are surprisingly few. The two most important 

 are probably the absence of reference to Whymper's 

 work on aneroids, from the chapter on altitude 

 determinations, and to C. Reid's explanation of the 

 formation of the chalk coombes, from the discussion of 

 the origin of dry valleys. 



The work is divided into three parts, dealing respec- 

 tively with general morphology, the surface of the earth, 

 and the sea. Its plan is based on the conception of the 

 earth's surface as composed of a series of " earth-forms " 

 which range between the extremes of mountains and 

 valleys. The description and classification of these, 

 and the study of their origin and development, form 

 the subject-matter of geographical morphology. This 

 science, therefore, depends on the literature of geodesy, 

 geology, and geojjraphy. The book commences with an 

 outline of general morphology, which depends in the main 

 on the first of these. The chapters on mathematical 

 geography, and on morphography and morphometry, 

 are probably the most valuable of the five devoted to this 

 part of the subject. In these he states the latest con- 

 clusions upon various debated problems. He points out 

 NO. I 3 IS, VOL. 51] 



(p. 9) that the amount to which the form of the earth 

 deviates from an ellipsoid of revolution is between ± 200 

 and ± 250m. He discusses the relative value of the 

 various geoids, and expresses a preference for Northern 

 Europe, for Bessel's instead of Clarke's, which is used 

 in England. The principles of earth-measurement are 

 briefly considered ; the standard levels used in ditierent 

 countries are tabulated, and their relations to each other 

 shown. The value and method of construction of hyso- 

 graphic, klinographic, hypsoklinographic, and bathy- 

 graphic curves are shown. The difficulties in the 

 determination of altitudes caused by the uncertainties of 

 refraction are pointed out. The inevitable inaccuracy 

 of map lines is illustrated by a list of the lengths assigned 

 to a portion of the Istrian coast in a series of standard 

 maps ; the figures range from 105 km. to 22381 km. The 

 calculation of the volumes of continents is considered, 

 and finally elaborate tables given of geographical 

 statistics. The ratio of land to water is taken as 2'54 

 (p- 97) ; the principal previous estimates are given from 

 the time of Riccioli, who in 1661 estimated that the land 

 was in excess in the proportion of S to 5. An interest- 

 ing sketch of the literature on " geographical homo- 

 logies " shows how early attention was drawn to the 

 remarkable parallels and contrasts in the distribution of 

 land and water. This part of the work concludes with the 

 consideration of the question of the permanence of oceans 

 and continents. Penck quotes Cayeux as if this author s 

 investigations proved the terrigenous origin of all the 

 chalk, and though he notices Blanford's arguments, he 

 does not seem to appreciate their full significance. His 

 sketch of the literature of the subject shows that, though 

 with some striking exceptions, the difference on this 

 question has been one between geologists on one side, 

 and geographers on the other. In this connection it is 

 interesting to note that Penck accepts (p. 167) the view 

 that the ocean floors have a higher specific gravity than 

 the continents, and places the difference, according to 

 Helmert's work, at •001 of the specific gravity. 



The second part of the book describes the surface ol 

 the earth, or the " Landoberflache." The first section of 

 this deals with the composition ol the earth's crust, and 

 the forces that act upon it. The figures given to illus- 

 trate Suess' terms are very clear and instructive ; the 

 table of geological systems is, however, out of date ; the 

 C^rdovician is not accepted, and the Tertiary and Quater- 

 nary are each regarded as etjual to such divisions as the 

 Trias and Permian. The account of the agents of denuda- 

 tion is very detailed and thorough. The hydraulics of 

 river action (pp. 259-385) is treated with especial care, 

 and the references to the literature of the subject include a 

 much wider range than is usual. The controversy as to 

 Baer's law of the influence of the earth's rotation on the 

 direction of rivers is clearly summarised, and the truth 

 of the law upheld ; great stress is laid upon the deepen- 

 ing of the Rhine on its left bank in the regulated por- 

 tions of its course. The author attributes to glaciers 

 considerable erosive power ; he maintains that the 

 characteristic featuie in erosion by ice, is that the ex. 

 cavations vary in depth with the strength of the rocks, so 

 that true rock basins are formed (p. 409). He still 

 accepts the glacial origin of cliques, and even approves 

 of Ramsey's views of the origin of some of the Alpine 



