432 NEW YORK STATE MUSEUM 



narrows on reaching this line but expands again into a swampy 

 tract which has probably been caused by glacial damming of its 

 headwaters. The same explanation of the Mariaville pond and 

 Featherstonaugh lake is offered. To the east the Poentickill heads 

 within a quarter of a mile of the Plotterkill which stream it must 

 eventually tap. 



The peculiar basin shape of the upper valley of the Sandseakill 

 very strongly suggests that this stream had matured before the 

 coming of the ice sheet during that period and that its lower course 

 has subsequently been cut through glacial debris and has not yet 

 affected the gradient of the upper valley. The presence of large 

 amounts of till throughout the lower course which has nowhere 

 reached the rock tends to substantiate this interpretation of the 

 topography. 



Stratigraphy 



North side of Mohawk. In order that the areal distribution of the 

 formations to be described in the present paper may be considered 

 along with the more detailed description of particular sections, the 

 order of treatment of the latter will be determined by their geo- 

 graphic distribution beginning with the most westerly on the north 

 side of the Mohawk river. 



Just west of the highway bridge across the Mohawk river at 

 Amsterdam is an excellent exposure in the north bank of the river 

 of the lower members of the Trenton stage. This point is imme- 

 diately beneath the yard of a large brick dwelling house that stands 

 near the river bank. The following layers are exposed. 



45A« Section just west of Amsterdam highway bridge 



A^ Level of yard. Massive crystalline lime- 

 stone, dark to grayish blue, weathering gray. 

 Highly fossiliferous. Abounding in Rafines- 

 quina alternata (Con.) Hall and Qarke. 

 Trenton. 8'=I4' lo'' 



A^ Irregular dark drab layer. 6''= 6' lo" 



A'' Light to dark drab of irregular lumpy struc- 

 ture. 9"= 6' 4" 



aThe system of recording localities employed by the department of geology of Union 

 university was as follows: when a new locality is visited it Is given a station number, 

 as 45 in the present case, which number indicates the order in which the locality was 

 first studied. Thus Amsterdam was the 45th locality visited under the present system. 

 The sections studied in any given locality are each given a letter, as A in the present 

 case, in the order of their study, and the various divisions of the section are num- 

 bered in the ascending order by primes, as A^, A», etc. 



