822 REVIEWS 



Geological History of New York State. By William J. Miller. 

 New York State Museum, Bull. No. 168, 1914. Pp. 130, 

 pis. 52, figs. 40. 



This bulletin is a brief summary of the geological history of the state. 

 It was the intention of the author to presuppose no scientific knowledge 

 of geology on the part of his readers, and that the work should be in 

 the nature of a textbook. A few pages in the introduction are devoted 

 to geologic processes and throughout the context an effort is made to 

 define technical terms. The reviewer does not believe the author 

 succeeded in making the report sufficiently non-technical to be popular 

 with laymen. It will serve better as a reference book for geologists 

 who wish a brief statement of some of the larger phases of the region's 

 history. 



The report is illustrated with many excellent photographs of uncon- 

 formities and other structural and physiographic features which abound 

 in the state. 



Unfortunately this report, in common with other New York reports, 

 does not contain a table of contents and its value as a reference book is 



impaired thereby. 



W. B. W. 



Origin of Hard Rock Phosphates of Florida. By E. H. Sellards. 

 Florida Geol. Survey, Fifth Annual Report, 1913, pp. 23-80, 

 pis. 9, map 1. 



The hard rock phosphates are found chiefly as bowlders and irregular 

 fragments in a formation of Pliocene age that the author has named 

 Dunnellson. The formation is rather heterogeneous but a phase of 

 light-gray sands is the usual matrix in which the phosphate rocks are 

 imbedded. 



Theories generally advanced to explain these deposits have involved 

 some form of guano alteration. The author believes the real source of 

 the phosphate was from phosphoric acid derived from the disintegration, 

 in situ, of overlying beds. The acid was borne downward by ground- 

 water, and replaced limestone, or was chemically precipitated. No 

 reactions are suggested for the latter process. The deposits are asso- 

 ciated with clay lenses and other conditions that interfere with the free 

 circulations of ground-waters. It is suggested that the presence of 

 precipitating agents may be the important factor here rather than the 

 retardation of ground-water circulation. The shattered and hetero- 



