234 C. P. BERKEY PALEOGEOGRAPHY OF SAINT PETER TIME 



the two seas in which the typical formations were accumulating. This 

 still further increases the difficulty of direct comparison and makes any 

 statement of exact correlation in terms of Chazy or Calciferous (Beek- 

 mantown) of doubtful value. The only method left is by the indirect 

 process of comparing the succession from a well established base of uni- 

 formly recognized formation. 



The formation best suited to this datum-plane use is the Black Kiver 

 beds. They have a more universal extent than any other of the lower 

 members of the series, in that they cross the New York divide ( Frontenac 

 axis) and are recognizable in both ancient seas. 



On the east side of the divide, in the ancient sea that occupied New 

 England and the eastern borders of New York, was laid down a contin- 

 uous series whose succession is as follows : 



Feet 



Black River 80 



Chazy * 800 



Beekmantown , 1,500 



Potsdam , 0-1,000 



Oi> the west side of the divide the Chazy and Beekmantown are not at 

 all or only partially developed. Their time equivalents are represented 

 in the formations and erosion intervals preceding the Black Biver beds, 

 as they overlap against the flank of the Adirondacks. The first one of 

 these below the Black Biver is the Lowville, resting on the basal con- 

 glomerate and Archean gneiss of the protaxis on the west side of the 

 Adirondacks. In the Mohawk valley some 400 or 500 feet of Beekman- 

 town rest on the pre-Cambric gneiss, followed after a pronounced erosion 

 interval by a few feet of the upper Lowville, which grade into the Black 

 River. As shown by well borings, successive members of the very ex- 

 tensive series of lower Ordovicic and Cambric sediments appear one below 

 another at greater and greater distance from the crystallines. Toward 

 the southwest there are prevailingly limestones and dolomites, consti- 

 tuting the Stones Biver group and Knox dolomite, which together attain 

 a great thickness. 



In the interior sea, the so-called Mississippian sea, there is a close 

 relationship of formations. There is, however, much variety in the series 

 along the margins, and the numerous breaks and oscillations make it 

 possible locally to subdivide minutely with success. In the deeper, less 

 disturbed, sea basin there was apparently continuous sedimentation and 

 a fairly uniform type of deposit resulted. Into this each marginal type 



* Brainard and Seeley : Bull. Am. Mus. Nat. Hist, vol.'viii, p. 30o. 

 American Geologist, vol. ii, p. 323. 

 Brainard : Bull. Geol. Soc. Am., vol 2, p. 293. 



