STKATIGKAPHIC VEKSUS TIME BASIS 111 



correlated with the Genesee shales, the beds following, for 1,200 feet, 

 are found to be dominated by an Ithaca fauna. This shows an extreme, 

 so far met with, of the limit of expansion of that fauna. 



DEVONIAN SECTION OF GENESEE VALLEY, NEW YORK 



In the third case — the section of the Devonian in the Genesee valley, 

 New York — the Ithaca fauna is entirely wanting, and is there replaced 

 by the Buchiola fauna of the Cashaqua, Gardeau, and Nunda (" Port- 

 age ") formations. In the Seneca Lake valley a slight trace of the Ithaca 

 fauna is seen above the Sherburne, but only slight. The Sherburne, 

 with its Buchiola fauna, is followed by the Ithaca (400 feet), containing 

 a rich and characteristic fauna, which is then followed by 600 feet of 

 Enfield shales, in which the Buchiola fauna again returns with some 

 modifications. 



GENERAL DISCUSSION OF THE THREE TYPICAL ILLUSTRATIONS 



The case of the Catawissa section, in which the Ithaca fauna occupies 

 an interval of nearly 1,500 feet, wherever fossils occur, is a striking illus- 

 tration of local difference in range of faunas, since the great thickness of 

 sediments through which the Ithaca fauna ranges can not be interpreted 

 as increase in thickness of sediments of that particular part of the section, 

 for the sequence of faunules is in its normal order from Genesee to 

 Chemung, but the Ithaca fauna (which is entirely wanting in the Gen- 

 esee section), there dominates over all associated faunas from near the 

 base to the top of the fossiliferous zone. 



The real problem before us may be presented by considering the first 

 case in detail. The chief facts are as follows : In New York there is a 

 standard set of formations occupying a particular portion of the geolog- 

 ical column, with which we are all familiar. The formations and their 

 relative positions in the stratigraphic scale are Oriskany, Corniferous, 

 Marcellus, Hamilton, Genesee, (" Portage " or) Nunda, Chemung, and 

 Catskill, together constituting the main part of the Devonian system of 

 that province. 



The United States Geological Survey geologic folios for Virginia and 

 West Virginia (take, as examples, the Stanton, Franklin, and Monterey 

 quadrangles) present the same portion of the geological column, divided 

 on a stratigraphic basis into the Monterey, Romney, Jennings, and Hamp- 

 shire formations. 



In the text of the Stanton folio equivalence is implied by a table in 

 which the divisions of the scale, with the names and symbols used in 

 the folio, are (in an adjoining column) filled with names which have 

 been used by various authors, as follows : 



