REVIEWS 279 



The Correlation of Geological Faunas: A Contribution to Devonian 

 Paleontology. By Henry Shaler Williams. [Bulletin of the 

 United States Geological Survey, No. 210.] Washington, 1903. 



In the investigation of geologic problems concerned with correlation, 

 two" fundamentally different concepts must be kept continually in mind. 

 The first of these has to do with rock strata, the media in which fossil organ- 

 isms are preserved, and the classification of formations; the second has to do 

 with fossil faunas or assemblages of organisms preserved in the rocks, and 

 the classification of time periods. In the broad correlation of geologic 

 formations the data furnished by the faunas are of prime importance, and 

 too much cannot be said of the value of exhaustive researches upon fossil 

 faunas as faunas. 



The paper by Professor Williams on The Correlation of Geological 

 Faunas is essentially a treatise upon the methods of investigation of fossil 

 faunas, in which the Middle Devonian fauna of the New York province, 

 characterized by Tropidoleptus carinatus, is especially used for illustration. 



In the first two chapters of the work, "The Principles of Correlation" 

 and the "Geological Expression of Faunal Migrations" are discussed in a 

 manner appHcable to any problem involving the study of fossil faunas. 

 Chapter 3 is devoted to an apphcation of the principles discussed in the pre- 

 ceding chapters, to an investigation of the history of the Tropidoleptus cari- 

 natus fauna. In treating of the "Shifting of Faunas" in chap. 4, illustra- 

 tions are again drawn from the Devonian faunas of the New York province. 

 The principles involved, and the effect of the shifting as expressed in the 

 faunas themselves, are fully discussed. In considering the "equivalency" 

 of formations in chap. 5, examples are taken from the correlation of the 

 Devonian formations of New York and Ohio. The sixth and last chapter 

 of the treatise is devoted to the "Bionic Value of Fossils." The application 

 of the data furnished by species, genera, etc., of organisms, for the classifi- 

 cation, not of rock formations, but of time periods, is discussed, and the 

 chapter closes with the statement of a proposed "bionic time scale." 



In this paper Professor Williams has assembled the more important 

 results, both material and philosophical, which he has secured in the course 

 of his long-continued investigations of the Middle and Upper Devonian 

 faunas of New York. Many of these results have been previously pub- 

 lished in various shorter papers, but here they are for the first time brought 

 together in compact form. The paper is full of suggestions and should be 

 studied by every student of fossil faunas. 



Stuart Weller. 



