^2 NEW YORK STATE MUSEUM 



been currently correlated with the " Hudson River," Lorraine or 

 Frankfort formations, mainly for the reason that they overlie the. 

 black (Canajoharie) shales, which were identified with the Utica 

 shale ; further because they are lithologically like the Lorraine beds ; 

 and, finally, because they seem to be continuous westward with the 

 Frankfort shale, the lower division of the Lorraine group as it was 

 hitherto understood. Recent investigations by the writer ^ have, 

 however, shown that this thick formation contains a fauna not 

 younger than Trenton, that the underlying black shale is not Utica 

 but early Trenton in age, and that these sandstones and shales are 

 only apparently continuous with the Frankfort of the Mohawk, the 

 Frankfort pinching out gradually eastward and the Schenectady 

 beds rapidly thinning out westward. The Schenectady formation 

 is therefore now considered as of middle and upper Trenton age. 



The life of this formation has proved to be an extremely pe- 

 culiar one. It consists of a few graptolites, brachiopods, cephalo- 

 pods, lamellibranchs, trilobites and ostracods of upper Trenton 

 aspect, with prenuncial Utica forms, but besides there occurs, in 

 certain layers, a profuse mass of fragments of new eurypterids 

 and seaweeds (Sphenophycus latifolius). Ten species of euryp- 

 terids, belonging to various genera, have so far bee;i recognized, 

 but it is obvious from fragments of sculptured pieces of integument 

 that the fauna was still greater. The seaweeds, the rapid alterna- 

 tions of shales and sandstones and the mud cracks indicate that the 

 great thickness of beds was deposited in shallow water, and the 

 uniformity of the formation shows that this water kept deepening 

 approximately proportional to the accumulation of the sediments. 

 The formation extends mainly from southwest to northeast in a 

 trough that is here termed the lower Mohawk or western trough. 



While at present the formation reaches only the southwestern 

 corner of the Saratoga quadrangle, its great thickness on the ad- 

 joining Schenectady quadrangle, and the fact that the strike of the 

 formation is in the direction of this sheet, leave no doubt that it 

 once extended much farther north, probably across the sheet, and 

 has since been eroded away. 



The edge of the formation forms now a low escarpment, shown 

 by the contour lines in the very southwest corner of the sheet, and 

 this, like the typical Helderberg escarpment, farther south, is clear 

 evidence of the former extension farther northward of the 

 formation. 



1 Op. cit., p. 50. 



