April 7, 1916] 



SCIENCE 



499 



rising areas, and the negative elements, the 

 dominantly sinking areas, of the K'orth Amer- 

 ican continent. The larger positive elements 

 for the world are given in maps on pp. 462 

 and 463. 



In the fifteen chapters devoted to the Paleo- 

 zoic era, seven to the Mesozoic and four to the 

 Cenozoic, the author reveals his familiarity 

 with the geologic history of North America 

 and its life, and here too he departs frequently 

 from the older methods of presentation. At 

 the first important occurrence of a group of 

 organisms he discusses its zoology, evolution 

 and in general its geologic occurrences, allud- 

 ing but briefly to them later under the sepa- 

 rate periods. For example, trilobites, brachi- 

 opods and all the moUusk classes are discussed 

 between the chapters on the Cambrian and 

 Ordovieian. Fishes are given a chapter to 

 themselves just before the Devonian discus- 

 sion, and here are considered all subclasses, 

 even though the dominant modern type of fish, 

 the Teleostei, do not make their appearance 

 until the Jurassic. There might be a differ- 

 ence of opinion as to the advisability of group- 

 ing the ccelenterates and echinoderms under 

 the old name of " animals with a radial sym- 

 metry" and of discussing all classes of these 

 together directly after the Ordovieian. 



After the general discussion of the Paleozoic 

 one chapter is devoted to the Cambrian, one to 

 " Trilobites " and one to " Shelled Animals." 

 The Ordovieian consumes one chapter, " Ani- 

 mals with a Eadial Symmetry " and the 

 " Silurian " each one. Then in succession are 

 discussed " Fishes and the Ancestors of Ver- 

 tebrates," " Devonian Time," " The Old Red," 

 " Carboniferous of Older Geologists and the 

 Mississippian Period," " Pennsylvanian-Per- 

 mian Periods," " Pise of the Land Floras," 

 a chapter on " Coal," and one on " The Ear- 

 liest Land Vertebrates." While the discussion 

 of coal is the best that has thus far appeared 

 in a text-book on general geology, a brief con- 

 sideration of the results of E. C. Jeffrey's 

 work on the origin of coal and a view of one 

 of his remarkable thin sections of coal would 

 have added much to the completeness of the 

 discussion. 



The Mesozoic opens with a consideration of 

 " The Triassic Period," which is followed by 

 a chapter by Professor Lull on " Dinosaurs." 

 Then follow in order " The Jurassic " ; " Am- 

 monites and Belemnites," a very brief chap- 

 ter; "The Comanchian"; "Chalk"; "The 

 Cretaceous Period and the Laramide Revolu- 

 tion." The four chapters of the Cenozoic are : 

 "' The Dawn of the Recent in Cenozoic Time " ; 

 " Evolution of Mammals and the Rise of 

 Mentality " (including a discussion in greater 

 detail of the evolution of the camels, horses 

 and elephants) ; " Pleistocene " and " Man's 

 Place in Nature," this last a 17-page discus- 

 sion of man, biologic and geologic. The lec- 

 tures close with a most concise and helpful 

 fourteen-page summary chapter — " Earth His- 

 tory in Retrospect." 



In the discussion of a period the author be- 

 gins with a brief presentation of its occur- 

 rence in its earliest known areas, usually 

 Europe. This is done by an account of the 

 advances and retreats of the oceans and the 

 mountain upheavals. Then follows a consid- 

 eration of North America in greater detail, 

 giving stratigraphic thicknesses and the paleo- 

 geography of the principal portions of the 

 continent. This is followed by a synopsis of 

 the life. The chapter is usually closed by a 

 brief discussion of the climate and the eco- 

 nomic products of sedimentary origin. The 

 many figures illustrating the invertebrate life 

 are commendably simplified for beginners by 

 having their technical names banished to an 

 appendix. Very seldom is the distribution of 

 deposits throughout the world noted. "We 

 would thus not look to this book to find if 

 Australia has Silurian deposits or China those 

 of Mississippian age. 



A pleasing innovation is the inclusion of 

 the portraits of famous geologists. William 

 Smith is given in the discussion of the Juras- 

 sic, the study of which in England led him to 

 the discovery of the principles underlying his- 

 torical geology. Lyell is given in the Ceno- 

 zoic, Suess in the Cretaceous, Murehison in 

 the Silurian and Sedgwick in the Ordovieian. 

 Of the North American workers Logan looks 

 upon us from the pages of the Archeozoic, Hall 



