ONONDAGA SALT GROUP. 107 



two miles north of the village of Springport, and are about five in number. The masses of 

 plaster are beyond all comparison larger than those to the north and the east, and of better 

 quality. The masses have all been denuded, for they are surrounded and covered by the 

 most modem or the upper alluvion of Chittenango, presenting none of their terminal associates, 

 if we except a portion of the mass in which they were enveloped, whose layers cover portions 

 of the gypsum. This is blackish in color, earthy in aspect, often variegated like the gypsum, 

 contains sometimes lamellar gypsum, and more rarely a little pure sulphur. It has the appear- 

 ance of an impure gypsum, and is considered by the quarrymen to be an incipient plaster, 

 requiring time only to make it perfect. The gypseous masses there are all in a low position, 

 some of them several feet below the surface of the lake. They show a thickness of from 

 fifteen to twenty-five feet, and some of them are opened along a line of two and three hundred 

 feet. The quarries furnish about ten thousand tons yearly ; the price of which, delivered at 

 the head of the lake, is from one dollar and fifty cents to two dollars the ton. A considerable 

 portion of this plaster is sent to Pennsylvania, by the Ithaca and Owego railroad and the Sus- 

 quehannah river. 



At Cayuga bridge, the plaster appears both above and below the bridge. The layers which 

 cover the masses are soft and light-colored, showing a few of the small irregular cavities 

 coated with dark-colored carbonate of lime, which, in the three plaster counties, are more com- 

 monly seen with the upper range of gypsum, and accompanying the shale of the group 

 throughout the third district. 



The Fourth or Magnesian Deposit, so called from presenting the needle-form cavities, or 

 fine striated columnar appearance, caused by the crystallization of sulphate of magnesia 

 before the rock had assumed its sohd state. These cavities were noticed the first year of the 

 survey, in the brownish drab rocks at Seneca falls, which cover the gypsum. They were 

 next seen in the same position as inferred, south of the plaster masses on the road from 

 Cayuga bridge to Springport, the rock being of the same kind ; that is, a brown drab in color, 

 solid, dull and fine grained. This same mass appears just beyond the north point of the 

 curve of Springport on the lake, rising a few feet above the water, and dipping to the south 

 apparently, so as to pass under the water-lime group, a part of which appears at the point. 

 They also appear in the foundation of the mill at Troopsville. Some of the cavities are three 

 inches in length ; the upper layer, which contains them, is brownish, and the lower one 

 bluish, the latter with more hme than usual, and its fracture conchoidal. But two layers 

 only are exposed. The same cavities also appear below the water-hme group, by the side 

 of Spht-rock railroad near Syracuse. The rock is in thin layers, and the cavities occur at 

 the joints, etc. ; under which there is a light tea-colored shaly mass. 



The mass at Reed's and Brewster's already noticed, may be referred to this deposit ; and 

 also those near Cedarville in Herkimer county. The difference between the third and fourth 

 deposits consists in the presence of these peculiar cavities in the latter, and the layers being 

 more solid and thick, the softer marls, etc. having terminated with the third deposit. 



These cavities are not confined to this rock ; they occur abundantly in the Niagara lime- 



