498 



SCIENCE 



[N. S. Vol. XLIII. No. 1110 



destructive processes are designated weather- 

 ing, as if there were no mechanical weather- 

 ing, but this oversight is later corrected (p. 

 19) by the assertion that both mechanical and 

 chemical processes fall under the head of 

 weathering. Talus is described as having the 

 coarser fragments above and the finer par- 

 ticles below (p. 22). As a matter of fact, true 

 talus deposits, as distinguished from alluvial 

 cones, are fine above and coarse below. " Bed- 

 rock " and " country rock " are defined as 

 synonymous (p. 19). "Bedrock" should refer 

 to soHd rock in situ as distinguished from 

 the unconsolidated superficial mantle rock. 

 " Country rock " should be applied only to an 

 older rock or rock complex, which has been in- 

 vaded by younger veins or eruptive bodies. 

 The distinction between base level and grade 

 does not seem to be clearly brought out (p. 

 66). A hase level is a level which controls the 

 downward cutting of one or more streams. 

 The control is such that each stream can re- 

 duce the inclination of its channel to a certain 

 slope below which further downward cutting 

 is impossible. This slope is grade. Only the 

 lower end of such a graded stream can actually 

 reach base level. 



After all is said, these imperfections are of 

 relatively minor importance, and they do not 

 seriously • detract from the usefulness of the 

 volume as a text-book. If " Physical Geol- 

 ogy" is also intended for a reference book — 

 and such every elementary text-book should 

 be with regard to the matter which it treats — 

 its abbreviated table of contents and its in- 

 complete index are to be deplored. In the 

 table of contents should appear all the center 

 and side headings employed in the text. In- 

 stead, merely chapter headings are given. 

 Nothing described or referred to in the text 

 should be omitted from the index. Tet coal, 

 outwash plain, bedrock, country rock, etc., are 

 not to be found. It is to be hoped that in a 

 second edition the writer wiU correct these 

 two grave defects. 



Part II. — Professor Schuchert has given us 

 a very readable, up-to-date book from the first 

 chapter on " Matter and Organisms " to the 

 last on " Earth History in Retrospect." It is 



unique in its method of treatment but with a 

 uniqueness that appeals. The book consists of 

 a series of lectures upon the principal events, 

 physical and biologic, in the history of the 

 earth. Each lecture or chapter deals with a 

 single subject. 



The ground is prepared for a clearer under- 

 standing upon the part of the reader by the 

 first seven chapters, " Matter and Organisms " ; 

 " Evolution, the Constant Change of Living 

 Things " ; " Fossils, the Geologist's Time 

 Markers " ; " The Geological Time-table " ; 

 " The Lands and Their Life " ; " Oceans, 

 Their Deposits and Their Life " ; " Seas, 

 Their ITature and Deposits." There follow 

 two chapters on the solar system, " Evolution 

 of the Stars and the Solar System" and 

 " Origin of the Solar System under the 

 Planetesimal Hypothesis," the latter by Pro- 

 fessor Barrell of Tale. In these chapters the 

 planetesimal hypothesis of Chamberlin and 

 Moulton is accepted as coordinating more 

 known facts of the entire solar system than 

 any other thus far propounded. The next 

 chapter, " Primordial Geologic Time " applies 

 this hypothesis more directly to the earth and 

 its known rocks. 



With the succeeding chapter begins the dis- 

 cussion of the history of the sedimentary rocks 

 of the earth and their included organic re- 

 mains, a consideration of the somewhat un- 

 stable continents and the ever encroaching 

 oceans. The author, though in his research 

 work advocating the uniform " ic " endings 

 for the period names, very wisely in this 

 undergraduate text-book uses the older end- 

 ings, the endings used in the publications of 

 the national surveys of the United States and 

 Canada, of nearly all state surveys and by the 

 majority of other geologists. There are three 

 chapters devoted to the pre-Cambrian, " The 

 Archeozoic Era " and " The Early and Late 

 Proterozoic Sub-eras." ISText is one on " The 

 Paleozoic Era," in general, in which is briefly 

 given the larger features of the North Ameri- 

 can continent during this era, especially a con- 

 sideration of the more permanent land and 

 water bodies. This includes a map (p. 577) 

 giving the larger positive, or predominantly 



