Cushing — Geology of Cunton County. 56] 



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topographic similarity. They lie well to the eastward of the Treadwell bay 

 exposures, as though shifted by a fault. If that be not the case, they arc at 

 a higher horizon. 



Hocks of Uncertain Age. Closely adjoining these Cumberland head 

 slates on the w est, are hard, grey dolomites, which form occasional knolls 

 protruding above the general surface. In one of the exposures, limestone 

 bands occur, which are full of fossil fragments, and similar to the bands 

 described from the upper Calciferous in Peru, just north of Valcour. These 

 rocks would be unhesitatingly classed as Calciferous, were it not for their 

 position. It seems certain that they must belong to that group, and they are 

 so represented on the map. Yet they are separated from the main exposures 

 of the Calciferous in central Beekmantown by a wide valley in which no 

 exposures occur, while the topography gives no indication of a fault between 

 them and rocks close at hand on the east, which lie at least 1,500, and 

 probably 2,000 or more feet higher in the section. This may be the line of 

 the Beekmantown fault. It is at least certain that throughout this territory 

 the entire Chazy is faulted out. 



Along the lake shore, from the extreme end of Point an Roches, south- 

 ward to the lighthouse, are pretty continuous exposures of blue and black 

 limestones, at times somewhat slaty, but ordinarily massive. They are very 

 barren of fossils, holding Lepet-ditia in some layers but little else, so far as 

 found. The top layer at the Point is charged w ith marcasite and contains 

 Leperditia and a Holopea-like gasteropod, abundantly. The section has con- 

 siderable thickness; just how much, remains to be determined, but one hundred 

 feet is a very modest estimate. The writer is unable at present to indicate 

 the precise stratigraphic position of these rocks. Mi-. Van Engen writes that 

 the Leperditia layer at the Point recalls the basal bed of the Black River lime- 

 stone on Button Bay island, and is disposed t<> correlate it with that, and to 

 regard all the rest as of Chazy age. A\ nile this is quite probably the proper 

 interpretation, the entire lack (or apparent lack) of the fossils which elsewhere 

 in the county abound in most of the upper Chazy, is an objection to it. The 

 rock closely resembles some beds found in the upper Chazy, but they 

 nowhere exhibit anything like the thickness shown here. It is therefore 

 thought that we may here have beds of Trenton age not met with elsewhere 

 in the county, occupying a position either just above, or just below the 

 Cumberland head series, and they are provisionally indicated as such on the 

 map. If they are of Chazy age there must be a considerable fault between 

 them and the Trenton slaty limestones north of Long point. 

 36 



