56 NEW YORK STATE . MUSEUM 



sandstones and the Oneida conglomerate, the materials consisted 

 largely of the coarser detritus washed down by rapid streams and 

 deposited close to the shores. The Medina, however, contains 

 much shale near the top. The Niagara formations are mainly 

 shale (Clinton and Rochester) and dolomite (Lockport and 

 Guelph). During Clinton time, the waters were probably rather 

 shoal with off-shore bars sheltering them from the sea as indicated 

 by the precipitation of iron ores along with sandstones, shales and 

 limestones. The formations up to the Guelph had been deposited 

 along a nearly east-west shore line that lay to the south of the 

 Canadian and Adirondack highlands ; they are now found in belt- 

 like areas extending across the central and western parts of the 

 State. In the Cayugan period the zone of sedimentation extended 

 into southeastern New York on the shore of the Appalachian pro- 

 taxis. The Salina shales formed at the opening of the period are 

 characterized by the deposits of rock salt and gypsum which prob- 

 ably resulted from the evaporation of the sea waters in confined 

 basins. The succeeding formations include the Cobleskill, Rondout 

 and Manlius limestones. The Medina sandstone at the base of 

 the Upper Siluric is one of the more important building stones 

 in the State and the various limestones named find utilization for 

 lime, cement or constructional purposes. 



The change to Devonic time was very gradual and no break 

 occurred in the sedimentation. In the first or Helderbergian period 

 the deposits were mainly calcareous and restricted to the central and 

 eastern parts. The Oriskanian period began with limestones, but 

 afterward the Oriskany sandstone, a very persistent, chiefly arenace- 

 ous, formation was deposited. To Ulsterian time belongs the Onon- 

 daga limestone, one of the very important calcareous formations, 

 largely quarried in the central and western sections. With the 

 Erian period began the accumulation of the great series of Devonic 

 shales and sandstones that spread over the whole southern plateau 

 section of the State from the Catskills and Helderbergs west to the 

 Pennsylvania border. The sandstone members are the bluestone 

 quarried for flagging, curbing and building stone and range in age 

 from the Hamilton in the Erian period to the Chemung at the top 

 of the Devonic. In the Senecan period occurred an interval of 

 limestone deposition in the central part represented by the Tully 

 limestone. 



The Carbonic era introduced at the start no marked variation in 

 the sedimentation. The representatives include shales and sand- 

 stones with conglomerate at the top ; the last being the equivalent 



