364 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Fossils recurrent in New York. — Those which this limestone pos- 

 sesses in common with the Niagara group are as follows : — 



Catenopora escharoides. Stromatopora concentrica. 

 Favosites niagarensis. Spirifer crispus. 

 gothlandica. 



Four of its fossils appear in newer formations and two in the 

 older, exclusive of the Niagara. (See Table No. IX. in the Ap- 

 pendix). 



Onondaga-Salt group. 



Mineral Character. — This group consists of successive beds of 

 argillaceous shales, marls, and shaly limestones, with brine-springs, 

 and gypsum in beds and veins. 



The prevailing colours are light-ashen and bluish-green ; but the 

 lower part of the group is deep red with spots of green, very like 

 the shale of Medina Sandstone. 



Vanuxem, in whose geological district this group is well seen, 

 divides it into four parts in the following order, beginning from 

 below : — 



1. Red shale with green spots. It is blood-red, fine-grained, 

 earthy in fracture, and without regular lines of division. Although 

 it is of vast extent, and from one to five hundred feet thick, yet no- 

 where has a fossil been discovered in it, or a pebble, or anything extra- 

 neous, except a few thin layers of sandstone, and its different-coloured 

 shales and slate. 



2. Alternate beds of red and green shale. This consists of shales 

 and calcareous slate of a light-green and drab colour, well seen near 

 Lenox Turnpike. We have at the top of the series green, then red 

 under it, alternating, downwards, with a little white and greenish 

 sandstone, and finally red shale, as the lowest visible mass. 



This second mass or deposit varies in its colours with the locality. 

 Here gypsum occurs in fibrous masses, in reddish or salmon colours, 

 peculiar to this No. 2 ; but its quantity is small. 



This second deposit, as well as the third, are exceedingly permeable 

 to water ; so that wells on the hilly parts of the country are useless. 



3. The third or Gypseous Deposit. — Two ranges of insulated 

 masses of gypsum, called beds, in thin bands of argillaceous lime- 

 stone, light and dark green, or drab. 



It is only in this deposit No. 3 that we have positive evidence that 

 salt has existed in this group in a solid state. 



The great mass consists of rather soft, yellowish, drab, or brownish 

 shale and slate, both argillaceous and calcareous, harder and softer. 

 The whole is usually denominated gypseous marl. Some of the 

 more indurated kind, when weathered, looks as if it had been hacked 

 regularly with a cutting instrument, owing to joints in two direc- 

 tions, giving a rhombic surface. 



Dr. Beck found a considerable amount of magnesia in the mass 

 enclosing the lower range of plaster-beds. 



The dark colour of the gypsum, and of many of its associates, 

 appears to be owing to carbonaceous matter, as it becomes lighter by 



