THERESA DOLOMITE AND PAMELIA LIMESTONE 161 



sand crj'stals on a small scale. This same lithologic ^peculiarity is a 

 feature of the so-called Potsdam-Beekmantown passage beds farther to 

 the eastward, and, so far as m.y observation goes, is confined to that 

 horizon, not appearing in the Beekmantown above. 



In the lower portion of the formation the large Lingula previously 

 mentioned is abundant, a gastropod which has not yet been determined 

 occurs at all horizons, occasional cystid plates and traces of other fossils 

 are found, and fucoidal markings are frequent on the surfaces of some 

 layers. 



The general thickness of the formation over the quadrangle is from 

 60 to 70 feet. Like the Potsdam^ beneath, it thins to the west and appar- 

 ently also to the south, though widespread sand deposits hide the decisive 

 proof of the latter. In addition to this thinning because of overlap, it 

 has also suffered erosion at its summit, owing to uplift (apparently 

 slight) and wear during a lengthy time interval. For instance, it has 

 a thickness of but 20 feet near the north end of Perch lake (see map), 

 though recovering its normal thickness of 60 feet within a mile on each 

 side, and the diminution in thickness is by the wearing away of the upper 

 beds. Coincidently with this local thinning, the overlying formation 

 thickens, showing basal beds which are lacking on each side and plainly 

 owing their existence to the surface depression. 



PAMELIA LIMESTONE 



This is the most interesting formation in the section, since it repre- 

 sents the thinned edge of a formation which, while widespread elsewhere, 

 has not heretofore been recognized in New York and is probal)ly in exist- 

 ence in the state as a surface formation only in this immediate district. 

 Because of its wide separation from other areas where the formation 

 appears and because it represents only a small portion of the entire for- 

 mation, the giving of a local name seems justified, and in Pamelia 

 township the entire thickness and both contacts are exposed. 



The formation consists essentially of limestone, though the bulk of it is 

 not pure limestone. At its base is found a thickness of from 10 to 30 

 feet of sandstone and greenish shale, the sandstone being coarse but weak, 

 oMdng to calcareous cement, and somewhat pebbly at the base, while th<; 

 overl3dng green shales are both sandy and calcareous. Because of their 

 weakness, these basal beds are but seldom exposed, though they seem to 

 everywhere underlie the remainder of the formation and hence to repre- 

 sent a changing horizon, since the formation overlaps on the district from 

 west to east. 



The formation has a thickness of from 125 to 150 feet along the west- 



