64 NEW YORK STATE MUSEUM 



tion there. At Middleville, 13 miles to the southeast from Tren- 

 ton Falls, the Trenton is only about 100 feet thick, excluding the 

 passage beds but including the Lowville. From Middleville on to 

 Ingham Mills and thence to Canajoharie, the thinning goes on, but 

 much less rapidly. Now unquestionably a portion of this diminu- 

 tion is due to the interruption of subsidence, this interruption 

 being most pronounced at Canajoharie, thence diminishing both 

 eastward and westward, apparently much more rapidly westward. 

 But the writer is strongly impressed with the possibility, nay 

 probability, that it is in part due to a change in the character of 

 the sedimentation going eastward ; in other words that the upper 

 portion of the Trenton of the Trenton Falls section passes later- 

 ally, by increase in amount of shale and by disappearance of the 

 few heavy limestone layers, into what are here mapped as pas- 

 sage beds. A large part of the upper half of the Trenton at Tren- 

 ton Falls, judging from the descriptions of Prosser and White, 

 consists of alternating layers of thin limestone and shale contain- 

 ing few fossils, the whole being capped by the heavy, gray, crystal- 

 line limestone at Prospect. With a thinning out and disappear- 

 ance of this upper heavy layer, very slight change in what lies 

 beneath would give it typical passage zone character, and the 

 gradual downward encroachment of this zone might be very 

 effective in thinning the typical Trenton beneath. 



Comparison with the northern Adirondacks 



In the lower Champlain valley, on the New York side, the 

 Paleozoic section comprises the 



Potsdam formation, maximum thickness unknown but 



Feet 



more than 800 



Beekmantown formation, maximum thickness 1800 



Chazy formation, maximum thickness 800 



Trenton (including Black river), thickness unknown, 



at least 250 



Utica shale, thickness unknown but great 



This section is at least 3000 feet thicker than that of the 

 Mohawk valley, and likely considerably more, the main part of 



