﻿Introduction. 



In the summer of 1900 the headquarters of the Cornell Sum- 

 mer School of Field Geology were at Trenton Falls, New York. 

 Four weeks were spent by Dr. H. F. Cleland, Mr. Tho. A. 

 Caine, and the writer, in a detailed study of the section exposed 

 in the gorge. In the course of the work we collected from each 

 layer, beginning with the lowest ; noted the relative abundance 

 of the more common species ; and saved specimens from each 

 layer for careful study in the laboratory. Unfortunately such 

 study has not yet been made ; but as this is the type section of 

 the Trenton, the writer has thought that perhaps it would be 

 worth while to give the following preliminary note in order to 

 show the range of the common species. The faunal lists are a 

 compilation from the note books which were kept separately, but 

 the writer is responsible for the grouping into faunules. The 

 sixty-eight divisions of the field work have been reduced to 

 sixteen.* 



Previous Work. 



Theodore G. White, in his Faunas of the Upper Ordovician 

 Strata at Trenton Falls, N. Y.,f gives a short account of the 

 literature of this section, and it is unnecessary to repeat it here. 

 Mr. White's paper contains a detailed section, but is the result 

 of hurried work at an unfavorable time of the year, November. 



He divided the section into twenty-three zones. Deducting 

 the first three, which are duplicated, there remain twenty faunal 

 zones, eleven of which are reported as containing more than one 

 species. Only one of these zones was considered sufficiently 

 characterized by any fossil or group of fossils to be mentioned 

 especially, and that was D21, which was called the zone of 

 Rafinesquina dclioidea. It was six feet in thickness and corre- 

 sponds to the top of M, just below the Rafinesquina deltoidea zone 

 of the present paper. 



After describing the Rathboue Brook and Poland Limekiln 

 sections, certain conclusions were drawn from a study of the 

 faunal lists. The first three are as follows : 



*My thanks are due to Dr. Cleland and Mr. Caine for permission to use 

 the notes. 

 |Trans. N. Y. Academy Sciences, Vol. XV, pp. 71-96, April 3, 1896. 



