28 NEW YORK STATE MUSEUM 



organic bodies in this rock are Orthocerata, some of which attain 

 the length of more than lo feet, and have a diameter of i foot or 

 more. Associated with these are several species of Cephalopoda 

 belonging to other genera, and some species oi Gastropoda which 

 subsequently appear in the succeeding limestone." These distinctive 

 features cause the formation to stand out as a clearly defined 

 horizon and there are many excellent exposures within the 

 quadrangle. 



Within the map limits the Black River limestone varies in thick- 

 ness from 6 or 8 to 15 or 16 feet and although it is so thin it 

 is persistently present. It is nowhere seen in outcrop on the Rem- 

 sen quadrangle although it does most likely occur. In the vicinity 

 of Little Falls it is occasionally present but only a few feet thick, 

 while at Canajoharie it is absent altogether. 



In connection with the Black River limestone certain erosion 

 features are noteworthy. Directly overlying the hard, massive 

 Black River beds are thin beds of Trenton with pronounced shale 

 partings. The latter beds are more readily worn back than the 

 former, the result being that the Black River nearly always stands 

 out as a terrace or platform back of which the Trenton rises rather 

 abruptly. This platform is of sufficient topographic importance to 

 be shown on the contour map. At times of high water the Trenton 

 is now being stripped off the Black River along Dry Sugar river 

 and along Black river a little over a mile above the mouth of Sugar 

 river. At the latter place the high water has cut back the Trenton 

 limestone so as to leave a distinct and remarkably regular platform 

 of Black River limestone which extends for several hundred yards. 

 During low water the river occupies a channel which has been worn 

 into the Black River limestone [see pi. 5]. 



The composition, texture, and massive character of the rock are 

 favorable for the development of " potholes." A magnificent dis- 

 play of "potholes" may be seen along Sugar river (Dry Sugar 

 river) from the canal crossing to near its mouth. The bed of the 

 stream, which is here dry except during high water, is literally 

 honeycombed vv^ith hundreds of *' potholes," some of them attain- 

 ing a depth of 6 or 8 feet and a diameter of several feet [see pi. 6]. 



Trenton limestone 



The Trenton limestone has its type locality at Trenton Falls 

 some 20 miles southward. From the standpoint of areal extent 

 and thickness this formation is the second most important one 



