MIDDLE AND tPPEE OEDOVICIAK 185 



Referring to Chapter III (p. 123) for the description of the Potsdam and "The- 

 resa" formations, we may quote Gushing ^"^^ on. the PameUa and LowviUe of the 

 Water town district (west of the Adirondacks) as follows: 



The Pamelia limestone is the most interesting formation in the section, since it represents 

 the thinned edge of a formation which, while widespread elsewhere, has not heretofore been 

 recognized in New York and is probably in existence 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 formation, 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 20 feet of sandstone and greenish shale, the sand- 

 stone being coarse but weak, owing to calcareous cement, and somewhat pebbly at the base, 

 while the overlying green shales are both sandy and calcareous. * * * 



The formation has a thickness of from 125 to 150 feet along the western margin of the 

 Theresa quadrangle and somewhat less than half that thickness on the eastern border. * * * 

 Above the sandy base the lower portion of the formation, 50 to-60 feet in thickness, is composed 

 of alternating beds of blue-black limestone, dove limestone, and gray magnesian limestone. 

 The beds usually run from 1 to 3 feet in thickness, though the black limestones may reach a 

 thickness of 10 to 15 feet. The upper half of the formation lacks the black limestone and 

 consists of alternations of dove limestone, gray magnesian limestone, light-gray to white thin- 

 bedded impure limestone, and yellow water lime. About midway of this upper half is a horizon 

 where the rocks have a pronounced pink tinge through a thickness of from 10 to 20 feet. Out- 

 side of the dove limestone beds, most of the material of this upper division is thin bedded, and 

 the abundance of light-colored layers sharply distinguishes it from the lower division. Near 

 the summit certain layers contain abundant nodules of coarsely crystalline calcite and sometimes 

 celestite as well. At the extreme summit are 10 to 15 feet of more massive beds of gray lime- 

 stone overlain by a thickness of a few feet of white impure beds which are somewhat sandy, and 

 these uppermost white beds are regarded as forming the base of the overlying Lowville forma- 

 tion. From base to summit the formation carries an abundant ostracod fauna. In addition, 

 the black limestones of the lower division carry a considerable additional fauna of gastropods, 

 cephalopods, corals, and trilobites. There is some evidence that, as the formation thins to 

 the east, owing to overlap, these black fossiliferous limestones occur at higher and higher 

 horizons, in fashion similar to the rise of the basal sandstone in the same direction. 



Many of the beds of dove limestone have mud-cracked surfaces. In connection with the 

 ostracod fauna and the presence of water limes, this seems to indicate shallow-water and closed- 

 basin conditions, similar to those which characterized the deposition of the water hme of the 

 Upper Silurian in the State ; but the fossiliferous limestones of the lower portion of the forma- 

 tion indicate that a period of open water, permitting the incoming of a marine fauna, preceded 

 the closed basin conditions. 



* * * [The Lowville] is a quite pure limestone formation, with a thickness of some 75 

 feet. The upper 20 feet are of pure limestone of blue or dove color and are exceedingly fossil- 

 iferous. Beneath follow 10 to 15 feet of thinner, more shaly limestones, with occasional fossils, 

 after which through 30 feet thickness appear alternations of these thin laj'-ers with thicker beds 

 of blue or dove limestone, with a basement of 10 feet of massive blue limestone, and then the 

 white shaly beds already noted as forming the base of the formation. * * * ^i^^ lower part 

 of the Lowville formation carries mainly an ostracod fauna, other forms being scarce, though 

 they do appear. ' ' But the lower Lowville Ostracoda include species of Leperditia and IsochUina 

 of much larger size than any so far observed in the underlying Pameha." " 



This local section is placed by Gushing ^"^ in comparison with those of the 

 Mohawk and Ghamplain valleys. 



a E. 0. Ulrich, letter of March 25, 1908. 



