GEOLOGY OF SARATOGA SPRINGS AND VICINITY 45 



Cryptozoon isC. proliferum, but in the upper beds another 

 and quite different species comes in. A bed of dove Hmestone which 

 occurs capping the upper, light colored dolomite to the west of 

 Saratoga, exposes this Cryptozoon most excellently (plates 9 and 

 10). The same species occurs at the summit of the formation at 

 Ticonderoga and elsewhere. The summit beds are usually full of 

 chert and the Cryptozoon is often heavily silicified. 



Unconformity at the summit of the Little Falls. The Little 

 Falls dolomite is directly overlaid, in the Saratoga region, by the 

 Amsterdam limestone of upper Black River age. No representa- 

 tives of the Beekmantown and Chazy groups appear in the section, 

 and the lower beds of the Black River group are also lacking. The 

 Tribes Hill limestone, which overlies the Little Falls in the Mo- 

 hawk valley and is of probable lowest Beekmantown age, is absent 

 about Saratoga. It may have been thinly deposited and subse- 

 quently eroded. It seems quite safe to say that the Beekmantown 

 and Chazy deposits never reached the district, and that the lower 

 Black River rocks were laid down but thinly if at all. 



Aside from the absence of these rocks from the region, the physi- 

 cal evidence of the unconformity is twofold. The base of the Am- 

 sterdam rests on quite different beds of the Little Falls, at the vari- 

 ous exposures of the contact, indicating erosion of the surface prior 

 to Amsterdam deposit; and the basal bed of the Amsterdam varies 

 from place to place, showing that the surface upon which it was 

 laid down was irregular and that the lower beds of the Amsterdam 

 are only found in the old depressions. Furthermore the Amster- 

 dam begins with a basal conglomerate full of Little Falls pebbles. 

 This basal layer is best seen at Saratoga. In the northern part 

 of the village, just west of the fault line and just north of where the 

 Delaware & Hudson Railroad crosses the fault, thin patches of 

 this conglomerate may be seen resting on the upper surface of the 

 Little Falls, proving that it is the very top of that formation which 

 there forms the upthrow face of the fault. 



AMSTERDAM LIMESTONE 



In the sections of the eastern Mohawk region there appears, 

 beneath the rocks which are strictly referable to the Trenton group, 

 a thin limestone formation which is wholly distinct from anything 

 found in the vicinity of Trenton Falls and which we regard as an 

 upper member of the Black River group and are calling the Amster- 

 dam limestone. A detailed account of the formation in the type 



