144 



NA TURE 



[July 29, 1922 



Geology," in two volumes — one with the sub-title 

 ! Geology," and the other with that of 

 " Historical Geology" — supports his reputation. His 

 work is marked by a logical arrangement of his material 

 and a clear and interesting statement of the main 

 problems. His teaching has been exceptionally wide 

 in its range, as he was first lecturer in mineralogy at 

 Tufts College, then professor of mineralogy and geology 

 at the Rensselaer Institute, and afterwards professor 

 of palaeontology in Columbia University, New York. 

 He has therefore had to teach both the physical and 

 biological sides of geology, and he writes on both 

 with sound knowledge and judgment. 



The course of study Prof. Grabau recommends is 

 to begin with the necessary elements of chemistry 

 and mineralogy ; then pass to the igneous rocks and 

 volcanic action ; next to take the " aqueous rocks " 

 which he limits to those formed as chemical precipitates, 

 excluding those due to the mechanical action of water 

 —and the organic rocks. Then follows the examina- 

 tion of the processes of erosion by wind, water, and 

 ice, and by organic agencies ; and after this work has 

 been dealt with he proceeds to their products, the 

 clastic rocks. The materials of the earth's crust 

 having been studied, the course proceeds to the 

 deformation of the rocks of the earth's crust by fold 

 and fault, and to metamorphism and the rocks made 

 by it, and concludes with the sculpturing of the earth's 

 surface. This scheme, according to Prof. Grabau, is 

 unusual in America, the physiographic section of the 

 subject being usually taken first, but though that 

 arrangement has no doubt great advantages in 

 secondary schools, and in the popular presentation of 

 geology, the author's course, beginning with the 

 primary rocks and their constituents, seems to be 

 the most logical for advanced students, and is adopted 

 in some British universities. 



The second volume deals with historical geology, 

 and is the section in which the author's previous work 

 renders his opinions of most interest and weight. 



One striking feature of the book is its wealth of 

 illustrations, which in the two volumes number 1980. 

 Some of the most original are diagrammatic sections 

 explaining the migrations of faunas, and they show 

 that colonies have often played an important part, 

 though not on the lines of the hypotheses which led 

 to this process 'having been so long held in well- 

 justified distrust. 



One interest of such a general text-book is its 

 evid as to progress towards international agree- 

 ment in terminology and theory. Prdf. Grabau's 

 classification ol the pre-Cambrian rocks shows that 

 their nomenclature is still chaotic, in the names of 

 ji, a ] , :tem : he regretfully uses the adjectival 



NO. 2752, VOL. I IO] 



ending of " ian," as in Cambrian, as a concession, but 

 he thinks the ending in " ic," such as " Cambric " will 

 ultimately be adopted. He quotes the use of the 

 term caldera for an explosion crater like Krakatoa, 

 and uses the term sink tor a hollow due to subsidence 

 for which caldera, the Spanish word, or its English 

 equivalent, cauldron, has prior right. His chapter on 

 vulcanism is illustrated' by an excellent map of its 

 distribution, but the Cameroons volcano should not 

 be entered as extinct. The chapter on petrology 

 makes no use of the American system, and the 

 author's conservative classification will probably 

 be found generally convenient for students of the 

 standard for which the book is intended. Tin' view 

 that the temperature of the centre of the earth may 

 be 200,000° or 350,000° F. is far in excess of the more 

 moderate temperature suggested by the probable high 

 thermal conductivity of the barysphere. 



The author discusses the cause of former glaciationSj 

 and considers that none of the theories is wholly 

 satisfactory. He objects to the theories based on 

 variations in composition of the atmosphere, on the 

 ground that their effects should be world-wide, whereas 

 the glaciations have been local. Apparently he seems 

 most disposed towards a theory of the shifting of 

 the poles, though recognising the weight of the mathe- 

 matical objections. He gives a diagram showing how 

 the movements of the North Pole into Greenland 

 would explain the glaciation in North America and 

 north-western Europe combined with the contemporary 

 freedom of Asia from ice. As a palaeontologist taking 

 especial interest in historical geology, his views on 

 the changes and positions of the ocean are of weight. 

 He admits great movements of the seas, but considers 

 that in the Palaeozoic period both the Atlantic and the 

 Pacific were shallow oceans ; he represents most of 

 the Atlantic as having been occupied by sea in the 

 Cambrian. He discusses at some length prehistoric 

 man, and adopts dates in years for him as if they were 

 well established ; but he is more cautious in his 

 reference to ' Piltdown man than some of his co- 

 patriots when dealing with the possibility of the skull 

 and the jaw belonging to the same individual. 



(2) Mr. C. K. Leith's book on the economic aspects 

 of geology contains many features of special interest. 

 The central part of the book consists of brief descrip- 

 tions of the chief ores and economic minerals, of their 

 industrial uses, geological features, and mode of 

 formation. The terseness of the descriptions makes 

 them all the more convenient for those who desire 

 a synopsis of the classification and formation of the 

 chief economic minerals. The classification places 

 pyrites amongst the group of fertilisers. This unusual 

 arrangement is due to pyrites being largely used for 



