is 95 . SOME NEW BOOKS. 61 



two previous sections of Professor Walther's " Introduction," an 

 account has been given of the conditions of the " Bionomy " of the 

 sea, and the conditions of life and action of marine animals. The 

 concluding volume describes " Lithogenesis " or the method of 

 formation of the various rocks that are now being built on the 

 surface of the earth. Professor Walther begins with a plea for the 

 more systematic study of this subject. He maintains that far more 

 can be learnt from an examination of the sedimentary rocks than is 

 generally thought. So far does he carry this, that he declares that 

 the history of the earth could have been written from the evidence of 

 the rocks alone, even if they had not contained any fossils. For this 

 to be possible, however, much greater precision is necessary in the 

 study of the methods of formation of rocks now in process of 

 deposition, and of the agencies by which they are laid down and 

 modified. He wishes, therefore, to raise this study into a science 

 which he calls " phenomenology." According to Walther this subject 

 has not been properly appreciated: he thinks that, just as there 

 is comparative anatomy and comparative botany, so there ought to 

 be a systematic study of comparative lithology. He draws a 

 close analogy between the study of rocks and animals : phylogeny is 

 studied by the methods of palaeontology, embryology, and comparative 

 anatomy, and Walther maintains that rocks should be regarded in 

 the same way ; thus petrography and stratigraphy are equivalent to 

 palaeontological history, the study of rock development as at present 

 going on takes the place of embryology, and the comparison of rock 

 structures and characters agrees with comparative anatomy. 



The author defines Lithogenesis, or Lithogeny, as the interpre- 

 tation of "fossil rocks" by the investigation of the recent rock- 

 forming agencies (p. 537). This, he says, is only the application of 

 the method of Ontogeny which has always taken the leading place 

 in zoology and botany. The work is divided into three parts :— 1st. 

 General lithogeny ; 2nd. The " Faciesbezirke " of the present, des- 

 cribing the different deposits of different areas on the earth ; 3rd. The 

 bases of a comparative lithogeny. In the first are described the 

 different methods of the destruction of old rocks and the formation 

 of new ones. The subject is well illustrated by numerous references 

 and verbal illustrations which compensate for the lack of figures, of 

 which there are only eight in the volume. The various agencies are 

 systematically classified ; thus the author divides denudation into 

 four kinds, that by the wind, which he calls " Deflation," that by 

 flowing water, or Erosion, that by glacier ice, or Exaration, and that 

 by the sea, for which he accepts the term Abrasion. The second 

 part of the work is the largest : it describes the different types of 

 deposits formed in different regions on the earth. Dr. Walther takes 

 first the four different zones that run round the earth, and describes 

 their most typical deposits. There is the Polar region with its 

 moraines, its bog-iron ores, and its guano ; the temperate region with 

 its different sets of deposits grouped according as they are formed by 

 Exaration, by Erosion, or by Deflation. Then follows the zone of 

 deserts, where the agency of the wind and deposits formed chemically 

 in lakes undergoing desiccation are most characteristic. Finally 

 come the Tropics, where red marl and laterite are the most widely- 

 spread deposits. Then follows an account of the rocks formed on 

 the mainland by volcanic action, or on its shores as sea-beaches, 

 sand-dunes, mud-flats, delta-deposits, and talus-banks at the foot of 

 cliffs. The next five chapters, dealing with sea-deposits, form one of 



