682 REVIEWS 



Silurian. By C. K. Swartz, W. F. Prouty, E. O. Ulrich, and 

 R. S. Bassler. Maryland Geological Survey, Baltimore, 

 Md., 1923. Pp. 794, pis. 67, figs. 27. 



This recently published volume on the Silurian of Maryland maintains 

 well the high standard set by the previous volumes of the Maryland 

 Geological Survey. 



Both the lithologic and faunal features of the Silurian rocks are 

 shown with a wealth of detail in a series of sections by Dr. Swartz and 

 Dr. Prouty. The more significant features of these sections are admir- 

 ably summed up in a preliminary chapter by Dr. Swartz which includes 

 two tables, one showing the formations, lithology, and faunal zones 

 recognized, the other indicating the increase in thickness of the sections 

 toward the east between Keyser, West Virginia, and the Delaware River, 

 Pennsylvania. 



The section on the correlation of the Maryland Silurian formations 

 with those of bther areas by Dr. Swartz includes two noteworthy features 

 — a table showing the history of geologic nomenclature in Maryland and 

 a tabular presentation of available knowledge concerning the range and 

 distribution in eastern America of the Maryland Silurian fauna. The 

 nomenclature used by eleven geologists, who during the past eighty-five 

 years have recorded their studies of the Maryland Silurian rocks, is 

 shown by the nomenclature table. The three stratigraphic subdivisions 

 made by the Rogers brothers in 1836 have expanded to twenty-four 

 divisions in the refined studies of Dr. Swartz and his associates. In the 

 present state of geologic nomenclature such a table might well be con- 

 sidered a valuable, if not an essential, feature of any elaborate or compre- 

 hensive stratigraphic paper. Without such an aid the geologist who is 

 not a specialist on the region or horizon discussed is likely, in the present 

 stage of the development of stratigraphy, to find in many recent papers 

 the highly localized nomenclature which refined work is now developing 

 obscure. Dr. Swartz has, in this report, retained only two of the seven 

 major divisions of the Silurian recognized by the Maryland Survey in 

 1897. This may lead the reader to speculate on the probable fate of 

 some of the names used in the present report at the hands of future 

 workers in the Maryland field. 



The history of the various classifications of the Silurian in America is 

 dealt with in a paper by Dr. Ulrich and Dr. Bassler. The references to 

 the Hterature omit mention of some important papers relating to this 

 subject. One of these by Cumings {Handbook of Indiana Geology) has 



