376 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,! 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.".^ Since the passage beds on 

 Grand isle are denionsitrably 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 to^vard 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.^ 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.^ 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. White 

 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 therefoTe 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, White gives the 

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

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

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



^Op. cit. p.114. 



^Op. cit. p.460. 



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



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



^Op. cit. p.456. 



