584 HENRY SHALER WILLIAMS 



name proposed for divisions of the second rank (i. e., subdivisions 

 of groups); third, series was the name for the third-rank divisions; 

 fourth, etage, for the fourth rank; and, fifth, assise for the fifth 

 rank. The terms, ere^ periode, epoque^ age were proposed for the 

 time divisions corresponding to the respective stratigraphic divisions 

 of the first Hst. In this scheme "systems" were the systems in 

 common use. Agreement as to which of the system names should 

 be retained was settled by the congress. Finally it was proposed 

 that all the names of each particular rank should receive the same 

 ending: -aire, -ique, -ian; and thus names show by their endings 

 the rank of the division to which they are applied. 



The fundamental difference from all this, seen in the rules of 

 the United States Geological Survey, is the adoption of a carto- 

 graphic unit and calling it "formation." 



The formation the unit in American classification. — In rule 2 it 

 is stated: "In all classes of rocks the cartographic units shall 

 be called 'formations.'"' A "sedimentary formation" is defined, 

 viz.: "Each formation shall contain between its upper and lower 

 limits either rocks of uniform character or rocks more or less uni- 

 formly varied in character. " In other words, the unit division 

 of stratigraphic rocks recognized for mapping, and hence for classi- 

 fication purposes, is a mass exhibiting unity of composition. Pro- 

 vision is made further in the rules for recognizing and mapping 

 "especially developed parts of a varied formation" and calling 

 them members, "i/ they have considerable geographic extent,''^ and 

 and lentils " i/ their distribution is more limited.'"^ 



The units of the time scale, however, are, by the United States 

 rules, said to be "periods" — the time equivalent of the standard 

 geologic systems (rules 14 and 15, p. 25), and "for purposes of 

 general correlation formations shall be referred to the standard 

 systems," principally by paleontology. Thus, in classifying and 

 correlating formations with each other, the physical units in the 

 United States are "formations," which may be gathered into aggre- 

 gates on the basis of correlation of their fossils with standard systems, 

 all of which are in fact represented typically in Europe; but they 



1 Twenty-third Annual Report, p. 23. 



2 Ibid., p. 24. 



