MINERAL RESOURCES OF THE STATE OF NEW YORK 263 



width into Madison county, while the strata are recognizable as far 

 east as Herkimer county. The Guelph, on the other hand, is 

 restricted in outcrop to a limited area in Wayne, Monroe, Orleans and 

 Niagara counties. In the vicinity of Rochester the general succession 

 consists of 62 feet of Lockport dolomite at the base, followed by 3 feet 

 of Guelph dolomite, 32 feet of Lockport and finally 8 to 10 feet of 

 Guelph at the top. The Lockport is rather thin bedded and siliceous 

 at the base, with more or less of bituminous shaly matter; the beds 

 thicken higher up and the topmost ones are fossil dolomite of fairly 

 pure nature. The color is dark gray to light gray for the fossil 

 variety which contains spots or blotches of red and has omam.ental 

 qualities when polished. Cavities and veins with crystallized calcite, 

 dolomite and other minerals are not uncommon. Quarries of 

 constructional stone have been worked around Niagara Falls, 

 Lockport and Rochester, and magnesian lime has been made from 

 the Lockport member in Niagara county and from the Guelph 

 near Rochester. Examples of the architectural use of the dolomite 

 are to be seen in Buffalo, Niagara Falls and other cities in the western 

 section of the State, 



The Cayugan group in the upper part of the Silurian system 

 includes a number of formations that are important for their limestone 

 beds. The Salina is mainly a shale formation but near the top 

 occur impure calcareous strata which are known as the Bertie water- 

 lime. The Cobleskill, Rondout and Manlius are largely calcareous 

 in character. 



The Bertie has its main development in the State within the 

 borders of Erie county, but it reaches into Genesee and Monroe 

 counties and is known as far east as Otsego county. It has been 

 extensively quarried for natural cement in Buffalo, Falkirk and 

 Akron; this industry is now discontinued and the quarries are 

 inoperative. The cement rock consists of a layer 5 to 8 feet thick 

 made up of drab or gray argillaceous limestone enclosed within dark 

 impure beds, of which the so-called " bullhead " stratum, a magnesian 

 limestone, has been used for cut stone. This bed has the strati- 

 graphic position of the Cobleskill formation^ (Coralline limestone 

 of Hall). 



The Rondout and Manlius limestones have supplied large quan- 

 tities of material for natural cement manufacture. The extensive 

 cement mines in the Kingston district are located in the Rondout, 

 as is also that formerh^ worked at Howes Cave, Schoharie county. 



^ C. A. Hartnagel, Preliminary Observations on the Cobleskill (" Coralline ") 

 Limestone of New York. N. Y. State Mus. Bui. 69, 1903, p. 1109-75. 



