206 CHARLES S. PROSSER 



geological formations was not closely scrutinized and there were 

 very few clearly denned rules governing the naming of the vari- 

 ous geological divisions. In general, the names referred to some 

 locality in which the rocks were more or less favorably exposed. 

 But this was not always the case, for not infrequently mineral- 

 ogical or paleontological terms were used for the names of the 

 divisions. Much the same system prevailed during the period 

 of the more active investigations of Dr. Orton and it is only dur- 

 ing the last few years that the movement has arisen to place the 

 nomenclature of stratigraphical geology on a basis similar to 

 that of the biological sciences. Two of the most potent influ- 

 ences in this movement are the International Congress of Geolo- 

 gists and the United States Geological Survey. The most 

 important principles of nomenclature governing the United States 

 Survey are : first, a formation is a lithological unit representing 

 the physical conditions of deposition, and should be called by 

 the same name so far as it can be traced and identified by means 

 of its lithologic characters aided by its stratigraphic associations 

 and its contained fossils. The formation shall receive a distinct- 

 ive designation, the preferred form being binomial of which the 

 first member is geographic and the other lithologic. When the 

 formation, however, consists of beds differing in lithologic char- 

 acter, so that no single lithologic term is applicable, the word 

 ''formation" shall be substituted for the lithologic term. The 

 second principle is the rule of priority. 1 These two princi- 

 ples of nomenclature have been very imperfectly observed in 

 most of our stratigraphical geology and as recently as Decem- 

 ber 1899, Dr. J. M. Clarke, state paleontologist of New York, 

 and Mr. Charles Schuchert published a revised classification of 

 the formations of New York in which a number of time-honored 

 names were replaced by new terms. 2 



REVIEW OF FORMER CLASSIFICATIONS 



In 1838 Professor C. Briggs, Jr., the fourth assistant geolo- 

 gist of the first geological survey of Ohio, proposed the name 

 'Tenth Ann. Rept. U. S. Geol. Surv., 1890, pp. 64, 65. 

 2 Science, N. S., Vol. X, 1899, pp. 874-87S. 



