36 NEW YORK STATE MUSEUM 



the 1 100 to the 1160-foot contour, we have here a thickness of 

 60 feet for the Little Falls formation with the summit not shown. 

 The actual thickness of the dolomite can not be determined, but 

 maximum and minimum limits may be fairly well fixed by con- 

 sidering the thickness of strata intervening between the bed of sand- 

 stone (already described) outcropping four-fifths of a mile north 

 of the north end of the village and the Trenton Hmestone in the 

 quarry west of this sandstone. The dip of both sandstone and 

 limestone is 10° west, with a horizontal distance of about 1150 feet 

 between them. The thickness of intervening strata is therefore 

 204 feet. Now if we subtract 60 feet for the known thickness of 

 the Theresa and 20 feet for the known minimum thickness (see 

 below) of the Black River limestone, this leaves 124 feet which 

 would be the thickness of the dolomite if the sandstone bed above 

 referred to lies at the summit of the Potsdam. If it lies at the 

 bottom of the Potsdam, then a thickness of about 50 feet must be 

 deducted from the 124 feet to leave 74 feet for the thickness of 

 the dolomite. Thus we conclude that the thickness of the Little 

 Falls dolomite lies between a maximum of 124 feet and a minimum 

 of 74 feet, with 100 feet probably not far from the actual thickness. 



Perhaps the best single outcrop which may be taken as typical 

 of the formation lies due west of the cemetery and near the base 

 of the formation where a thickness of 10 feet of dolomite beds is 

 shown (see plates 4 and 5). The beds range in thickness up to 2 feet 

 and contain numerous small cavities usually lined with dolomite 

 and clear quartz crystals of the common types so often found in 

 this formation in northern New York. Sometimes the cavities are 

 filled with white calcite. Scattered through the bluish-gray dolomite, 

 which has a fine-grained crystalline appearance, are many small, 

 water-worn silica grains, so that the rock is really a siliceous 

 dolomite. The ledge is divided into numerous small blocks by 

 well-defined nearly vertical joint planes. Some of the dolomite beds 

 near the summit of the rock terrace contain streaks of chert. 



No fossils were found in the Potsdam, Theresa, or Little Falls 

 formations. 



Absence of Beekmantown and Chazy limestones. Within the 

 Wells outlier there is no direct evidence for the presence or absence 

 of the limestones of the Beekmantown or Chazy formations. Heavy 

 Pleistocene deposits cover the critical places which might show such 

 rocks. These formations are not represented, however, except by 

 the Tribes Hill limestone in the Mohawk valley region and since 

 even the Tribes Hill practically does not occur within the Broad- 



