THE DEVONIAN SECTION OF ITHACA, N. Y. 583 



other rock, and at the same time there are no fossils found in them 

 which are known in other rocks beyond the group. "^ 



The taxonomic rank of the original subdivisions 0} the section. — 

 In geological literature subsequent to the publication of these reports 

 the geographic terms above mentioned have been appHed in a tech- 

 nical sense to subdivisions of the geologic column of varying taxo- 

 nomic value. Thus we find "Chemung group, period, series^ 

 beds, and formations;" and in the latest edition of Dana's Manual 

 of Geology we find "Hamilton period" described as consisting of 

 the Marceilus and Hamilton epochs (p. 576), and again the "Ham- 

 ilton group as composed of the Marceilus shale, Goniatite limestone, 

 Hamilton beds, and Tully hmestone (p. 593). 



Rules of classification and nomenclature. — Confusion of this kind 

 has made it necessary to construct definite rules for nomenclature 

 and classification in which the taxonomic rank of the subdivisions 

 is indicated. 



Two well-known examples of such rules are in use. The one 

 was proposed by the Congres geologique international; the sub- 

 stance of which was published as a report of the Commission pour 

 Vuniformite de la nomenclature^ made to the Berlin congress in 

 1885 by M. G. Dewalque, secretary of the commission. The other, 

 as finally perfected, was published in the Twenty-fourth Annual 

 Report of the Director of the United States Geological Survey in a 

 passage headed "Nomenclature and Classification for the Geological 

 Atlas of the United States" (pp. 21-27). The first may be said to 

 be the set of rules for the construction of the geologic map of Europe ; 

 the second, rules for the construction of the geologic map of the 

 United States. 



No attempt will be made in this place to describe either of these 

 sets of rules ; suffice here to explain a fundamental difference between 

 the two schemes. Dewalque 's scheme was an attempt to unify 

 the nomenclatures of the various nations of Europe by first estab- 

 lishing a set of names to distinguish the order of rank of the divisions 

 to which they were to apply. Thus, to divisions of the first rank 

 (i. e., the largest named divisions of the rock column) the term 

 "group" (French groupe) was applied; second, systeme was the 



I Geology of the Fourth District, p. 243. 



