162 H. p. CUSHIXG PALEOZOIC I>' XOETHAVESTERN XEW YORK 



ern margin of the Theresa quadrangle and somewhat less than half that 

 thickness on the eastern border. In the former situation are several 

 continuous sections of the lower 60 to 80 feet, but no section of the 

 entire thickness is known and no single thick section of the upper por- 

 tion. It seems superfluous to give detailed sections in this place. Above 

 the sandy base the lower portion of the formation, 50 to 60 feet in thick- 

 ness, is composed of alternating beds of blue black limestone, dove lime- 

 stone, 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 iDedded, impure limestone, and yellow waterlime. 

 About midway of this upper half is a horizon where the rocks have a 

 pronounced pink tinge through a thicl-cness of from 10 to 20 feet. Out- 

 side of the dove limestone beds, most of the material of this iipper 

 division is thin bedded, and the abundance of light colored layers sharply 

 distinguishes it from the lower division. Xear the summit certain layers 

 contain abimdant nodules of coarsely crystalline calcite and sometimes 

 celestite as well. At the extreme summit are 10 to 15 feet of more mas- 

 sive beds of gray limestone everlaid l)y a thiclaiess of a few feet of white, 

 impure beds which are somewhat sandy, and these uppermost white beds 

 are regarded as forming the l)ase of the overlying Lowville formation. 

 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 waterlimes, this 

 seems to indicate shallow water and closed basin conditions, similar to 

 those which characterized the deposition of the waterlime of the Upper 

 Silurian in the state: but tlie fossiliferous liinestones of the lower portion 

 of the formation indicate that a period of open water, permitting the 

 incoming of a marine fauna, preceded the closed basin conditions. 



LOWVILLE LlilBSTOXE 



The cit}' of Lowville is some 20 miles up the Black river from the 

 southwest corner of the Theresa quadrangle ; hence the district here is 

 near the t^'pe locality of tlie formation. As exhibited within the quad- 



I 



