Reviews — Outlines of Geologic History. 33 



REVIEWS. 



I. — Outlines of Geologic History, with especial reference to 

 North America. By Bailey Willis and Rollin D. Salisbury. 

 8vo ; pp. viii, 306, with numerous text-illustrations. Chicago 

 University Press and Cambridge (England) University Press, 1910. 



IN the Geological Magazine for July, 1906 (p. 328), we drew 

 attention to the very interesting History of American Geology 

 then published by Mr. G. P. Merrill. That volume dealt with the 

 gradual growth of knowledge, since 1785, historically and bio- 

 graphically. 



The present volume consists of "A series of essays involving 

 a discussion of geologic correlation presented before Section E of the 

 American Association for the Advancement of Science in Baltimore, 

 December, 1908". The symposium was organized by Mr. "Willis, 

 who also prepared the instructive series of pakeographic maps which 

 are interspersed in the text ; and the volume has been edited by 

 Professor Salisbury. It may be added that the several chapters have 

 appeared in the Journal of Geology, and are now bound together for 

 the convenience of geological students ; and that the volume will be 

 welcomed as containing the results of much research and important 

 philosophic suggestions with regard to the distribution of life in the 

 strata and the principles of correlation. 



Mr. C. R. Van Hise, in the opening chapter, deals with the 

 principles of classification, with the nature, sequence, and con- 

 tinuity of formations, and with unconformities and deformations. 

 He considers that pre- Cambrian rocks may be grouped into Archaean 

 and Algonkian, and that these two major divisions are general, 

 if not worldwide : the Archaean dominantly igneous, largely 

 volcanic and submarine ; the Algonkian mainly sedimentary, and laid 

 down when "essentially the present conditions prevailed on the 

 earth". The subdivisions of the Archaean into Laurentian and 

 Keewatin are purely lithological, the one consisting mainly of 

 plutonic acid rocks, the other largely of volcanic basic rocks. 



Professor Prank D. Adams follows with an essay on the basis of 

 pre-Cambrian classification, urging that a threefold division is 

 needed. He applies the terms Eo-, Meso-, and Neo-Proterozoic, the 

 first to the Archaean (of Van Hise), the second to Lower and Middle 

 Huronian, and the third to Upper Huronian or Animikie-Nastapoka 

 and Keweenawan-Athabasca. These three major periods are in the 

 opinion of Professor Adams separated by great unconformities or 

 epochs of diastrophism — epochs which afford " a basis of correlation of 

 great value and importance". Mr. Van Hise rightly objects to 

 a ' zoic ' classification, which is unsupported by fossil evidence. 



In the next essay Mr. C. D. Walcott discusses the evolution of 

 early Palaeozoic faunas in relation to their environment, and points out 

 that although the traces of pre-Cambrian life are very meagre, they 

 "are sufficient to indicate that the development of life was well 

 advanced long before Cambrian time began ". Thus the characteristic 

 fossil of the known pre-Cambrian fauna " is Beltina danai, a Crustacean 

 probably more highly organized than the trilobite. The associated 



DECADE V. — VOL. VIII. — NO. I. 3 



