38 NEW YORK STATE MUSEUM 



Ulrich, has led to the conclusion that they are at least as old as 

 upper Trenton and probably belong mainly between the middle 

 and upper Trenton. We therefore propose to distinguish this 

 formation as a separate unit under the term Schenectady formation, 

 its type exposures being at the Dettbarn quarries at Schenectady 

 and at Aqueduct and Rexford Flats near Schenectady. 



The conclusion of an age older than the Utica for the Schenec- 

 tady formation is supported by, or at once explains, the close con- 

 nection by transitional beds of the Canajoharie beds (which are of 

 lower to middle Trenton age) and these " Frankfort " beds of the 

 lower Mohawk valley, as shown in the section about Minaville and 

 along the Schoharie creek. 



The Utica shale, if it continued down the Mohawk valley, would 

 have to be found above the Schenectady beds. This inference is 

 supported by the fact that the latter are overlain by the Indian 

 Ladder shales (see page 50) which correspond in age to the South- 

 gate of the Eden group and are but little younger than the true 

 Utica. 



If one follows the foot of the Helderberg escarpment from the 

 typical exposures of the Frankfort shale down the Mohawk valley, 

 one meets but few rather widely separated outcrops of the barren, 

 olive gray Frankfort shales until one reaches the lower Mohawk 

 valley region, where the rather abrupt widening of the belt and the 

 thickening of the formation together with the appearance of much 

 calcareous sandstone (bluestone) combine to change greatly the 

 aspect of the " Frankfort " beds. The exact contact plane between 

 the Frankfort shales that thin out eastward and the Schenectady 

 beds that rapidly diminish westward, has not yet been established 

 and may be entirely buried in the deep drift plateau between the 

 foot of the Helderbergs and the Utica and Canajoharie exposures 

 in the lower reaches of the southern affluents of the Mohawk. 



The thickness of the Schenectady formation must be very great. 

 Cumings (title 44, page 466) has already found in the hill back of 

 Rotterdam a thickness of 1200 feet at least for the " Hudson River " 

 beds, for the top of the formation is not there reached. That the 

 thickness of the Schenectady formation is still considerably more, 

 is proven by the Altamont well-boring. In that well, the drill 

 started 595 feet below the top of the Indian Ladder beds and passed 

 through 2880 feet of sandstone and shales before reaching the 

 Trenton limestone. The shale formations have hence a total thick- 

 ness of 3475 feet there. The lowest 1200 feet of this may be 



