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NEW YORK STATE MUSEUM 



formation as mapped upon the Little Falls quadrangle. Sand hill 

 and vicinity are covered by very deep glacial drift so that no rock 

 exposures whatever may be seen to make the mapping certain. 



The characteristic absence of the Dolgeville shales over the 

 Remsen district as opposed to their presence over the Little Falls 

 district calls for an explanation. A careful comparison of the 

 sections in the two regions shows that the difference is probably 

 not as great as at first sight appears. The sections are here given 

 for comparison. 



Upper Trenton limestone 

 1 40 + ft 



Type section in the Trenton Falls district 



3 Utica shale J Thin bedded black shales somewhat calcareous at 

 300 + ft I base. (Sharp contact) 



h Thick bedded, coarse grained, gray 

 crystalline beds, 30 ft. (Fairly 

 sharp contact) 

 a Thin bedded, impure beds with pro- 

 nounced shale partings. 110 + ft. 

 (No sharp contact) 

 Lower Trenton limestone j Thin bedded, impure limestones with 

 1 40 + ft I thin shale partings 



Type section in the Little Falls district 



j Utica shale (as above) 



600 -I- ft (No sharp contact) 



2 Dolgeville shales ( Thin bedded, alternating limestone and shale 

 1 00 ft \ layers of about equal thickness. (No sharp 

 contact) 



1 Trenton limestone J Thin bedded impure limestones with thin 

 100 ft ( shale partings 



These sections show a rapid thinning of the Trenton southwest- 

 ward. Even when the Lowville and Dolgeville shales are included 

 with the Trenton proper in the Little Falls district, the thickness 

 is only 200 feet as opposed to nearly 300 feet for the Trenton 

 formation at Trenton Falls. This thinning continues southeast- 

 wardly to Canajoharie. Thus a slower rate of subsidence east- 

 ward while the limestones were forming was doubtless an im- 

 portant factor in causing the thinning in that direction. But as 

 Cushing has suggested, a change in lithologic character' of the 



