186 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Comparison with the Champlain and Mohawk sections. 



Gushing ^"^^ concludes: 



It has been shown that four formations — the Lowville, Pamelia, Theresa, and Potsdam — 

 are present underneath the Black River limestone in the Watertown region, and that there is a 

 great unconformity, both by erosion and by overlap, between the Theresa and Pamelia forma- 

 tions. The Pameha formation is of upper Stones River age, and [is] thus a formation hitherto 

 unrecognized in the New York section. It is thought that the unconformity mentioned can be 

 traced down the St. Lawrence Valley to the Champlain meridian and represents the expanded 

 western representative of the break discovered by Ulrich ia the Champlain Valley between 

 divisions A and B of the Beekmantown. It is also thought that it represents the proper line of 

 division for northern New York between the Cambrian and Lower Silurian systems, thus rele- 

 gating to the Cambrian nearly 400 feet of strata which have hitherto been classed as Beekman- 

 town. 



Prior to the recognition of the "Theresa" and Pamelia formations, described 

 above, the terms Beekmantown ("Calciferous"), Chazy, Lowville ("Birdseye"), 

 Black River, Trenton, and Utica were used. Their general distribution and rela- 

 tions all about the Adirondacks have been stated by Cushing.^"^ 



In 1910 Ulrich and Gushing ^^^^ published a detailed study of the Little Falls 

 dolomite of the Mohawk Valley, in course of which they developed the relations 

 between the Little Falls dolomite and overlying strata. They class the dolomite 

 as the uppermost Saratogan and separate it from the Beekmantown, with which 

 it has hitherto been placed. They describe an unconformity at the top of the 

 dolomite and take the plane of that unconformity as the basis of classification. 

 They say : 



Our comparative study of the region has, we think, made clear the correlation of the Calcifer- 

 ous of the Champlain and Mohawk valleys and seems to us also to show that the Little Falls 

 dolomite (division A and the lower part of B) does not properly belong with the Beekmantown, 

 either structurally or f aunally, and has been heretofore classed with it simply on the basis of sup- 

 posed lithologic resemblance; that it is separated from the remainder of, or rather the true 



