390 



m;\v stork state museum 



southward, so that the rocks disappear through thinning at the 

 upper eud of the Champlain valley, the middle division of the 

 formation being the last to vanish. Following the deposit of 

 the upper beds, uplift ensued, or at least a cessation of sub- 

 sidence and of deposit; there is little or no indication of wear 

 at the Chazy summit, so that the surface could not have been 

 raised much, if any, above sea level. 



The large amount of subsidence on the northeast during Pots- 

 dam, Beekmantown and Chazy times must have involved that 

 entire section of the present Adirondack region, since the Pre- 

 cambric floor of the district was not vastly irregular, nor 

 could its seaward inclination have been great. The amount of 

 rock thickness of these three formations which was deposited 

 in the lower Champlain valley was from 3500 feet to 4500 feet, 

 so that the upper Chazy deposits must have been carried far 

 into the present heart of the Adirondacks by their overlap on 

 the old land slope. 



During Chazy times the Cassin elevation on the south and 

 west sides of the region persisted, and no deposits of Chazy age 

 were formed. The land was in fact sufficiently elevated to per- 

 mit a certain amount of erosion of the Beekmantown deposits 

 which formed its surface. The uplift was accomplished without 

 tilting or folding of the rocks, except in a very minor degree, and 

 in general the Lowville rocks appear to overlie the Beekman- 

 town conformably. In some sections, as at Canajoharie, there 

 is a plain discordance in dip between the two formations, owing 

 to a very slight folding of the Beekmantown [pi. 7] ; but in most 

 places nothing of the sort can be made out, though a compari- 

 son of several sections usually suffices to show that the Lowville 

 does not always rest on the same bed of the Beekmantown. The 

 surface was planed down to great evenness, arguing for either 

 a long continued period of wear or else for a very low altitude 

 and gentle surface slope. 



The uplift of the northeastern region at the close of the Chazy 

 was coincident with, or somewhat closely followed by, a move- 

 ment of downward character on the south and west, which 

 much diminished the land area there, bringing the shore line in 

 close to the present Precambric margin of the region. The 



