62 On the Acid Spriiiya and Gypsum Deposits uf tht 



of a large portion of the overlying strata. In one case ob- 

 served by Mr Murray, a slender cylinder of gypsum passes 

 through several beds of the limestone, and at last terminates 

 in a cone of the usual form, which is entirely superior to the 

 limestone formation and surrounded by the tertiary clay of 

 the region. The comparatively recent origin which this 

 assigns to the gypsum deposits, is confirmed by the common 

 experience of the people of Western New York, where it is 

 a well known fact that since the settlement of the country, 

 walls have been disturbed and houses raised from their 

 foundations by a gradual elevation of the surface, where sub- 

 sequent examination has shewn the presence of domes of 

 gyjisuiii. 



On comparing these facts with those observed in connection 

 with the acid spring, it appears probable that the origin of 

 the gypsum is to be ascribed to the action of such mine- 

 ral waters upon the calcareous strata. How far the pres- 

 sure at a great depth may operate in preventing chemical 

 changes, we may not know, but it is easy to see that once 

 coming to a situation where it could act upon the limestone, 

 it would evolve carbonic acid gas, and form a calcareous 

 sulphate which from its sparing solubility would be at once 

 deposited in a crystalline form, while the water would pass 

 off saturated with the sulphate, and at the same time carry- 

 ing with it the soluble sulphates of magnesia, alumina, and 

 iron, which would be formed from the other bases generally 

 present in the limestones of this region. li' the amount of 

 acid were copious, or the supply of calcareous matter limited, 

 the water might rise to the surface with free acid, as in the 

 cases already noticed, and when the deposition of calcareous 

 sulphate had extended so far as to protect the carbonate from 

 farther action, the water would appear with a much smaller 

 portion of basis than before, having only the sulphate of lime, 

 which it could dissolve from the sides of its channels. 



If, on the contrary, the acid were entirely neutralized, the 

 spring would present at the surface the character of an or- 

 dinary bitter saline, containing calcareous and magnesian 

 sulphates ; two springs of this character are indeed found in 

 tlie same formation not far from here. The ferruginous and 



