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NEW YORK STATE MUSEUM 



Grand isle, directly opposite Cumberland head, and it would seem 

 that these are the rocks referred to as transition beds by Pro- 

 fessor Perkins. 1 From the study of the fauna White seems to 

 be somewhat uncertain as to the precise horizon, and speaks of 

 it as " very high Trenton or Utica". 2 Since the passage beds on 

 Grand isle are demonstrably such, a comparison of their faunas 

 with those of the Cumberland head rocks should settle the ques- 

 tion of stratigraphic equivalency. But, if these be actually the 

 passage beds, their thickness is apparently large, though the Cum- 

 berland head section is so greatly disturbed that little exact idea 

 as to its thickness can be obtained. The lithologic character 

 would seem to agree with such a reference. 



Published data of precise character in regard to the thickness 

 and nature of the Trenton toward the upper end of the lake, are 

 not numerous. On the Vermont shore, across the lake from Port 

 Henry, Brainard and Seeley give a measured thickness of 314 feet 

 for the Trenton, the exposures being a continuation of the section 

 on Crown point, on the New York side. 3 It is in this section 

 that the Black River limestone attains its maximum thickness of 

 71 feet. White says of it that, on Crown point, above the Black 

 River, is a continuous series of 100 feet of alternating, compact, 

 sandy and shaly layers, all quite thin, containing the lower and 

 middle Trenton fauna of the region. 4 It is not clear from their 

 account, whether Brainard and Seeley include the Black River in 

 their statement of the thickness of the Trenton or not. Wliite 

 states that there is a hiatus between the upper Trenton bed ex- 

 posed and the Utica outcrops beyond, but makes no statement 

 in respect to its amount. Nothing is therefore apparent as to 

 the transition beds in the region. But, unless a fault intervenes, 

 it would seem that they can not be of very considerable thickness. 



At Larrabee point, opposite Fort Ticonderoga, Wliite gives the 

 Trenton a thickness of 110 feet, the section terminating in that 

 formation, though Utica shale appears in place not far away. 5 The 

 lithologic character of the formation is not touched on, and we 



*Op. cit. p. 114. 

 -Op. cit. p.460. 



3 Am. Mus. Nat Hist. Bui. 8:313. 

 4 Geol. Soc. Am. Bui. 10:457. 

 °Op. cit. p.456. 



