248 



PALAEOZOIC TIME UPPER SILURIAN. 



sected by shrinkage-cracks, — effects of the drying of the mud of the 

 ancient mud-flat by the sun. 



Minerals. — The gypsum does not constitute layers in the strata, 

 but lies in imbedded masses, as shown in the annexed figures. 



415. 



416. 



The lines of stratification sometimes run through it, as in fig. 416 ; 

 and in other cases the layers of the shale are bulged up around 

 the nodular masses (fig. 415). Both cases show that the gypsum 

 was formed after the beds were deposited. Sulphur springs are now 

 common in New York, and especially about Salina and Syracuse. 

 Dr. Beck describes several occurring in this region, and mentions 

 one near Manlius which is "a natural sulphur-bath, a mile and a 

 half long, half a mile wide, and 168 feet deep, — a fact exhibiting in 

 a most striking manner the extent and power of the agency con- 

 cerned in the evolution of the gas," and showing, it may be added, 

 that the effects on the rocks below must be on as grand a scale. 

 These sulphur-springs often produce sulphuric acid by an oxyda- 

 tion of the sulphuretted hydrogen. There is a noted "acid spring" 

 in Byron, Genesee co., N.Y., connected with the Onondaga forma- 

 tion, besides others in the town of Alabama. This sulphuric acid 

 acting on limestone [carbonate of lime) drives off its carbonic acid 

 and makes sulphate of lime, or gypsum ; and this is the true theory 

 of its formation in New York. The laminae which pass through 

 the gypsum unaltered, as in fig. 416, are those which consist of 

 clay instead of limestone. The gypsum is usually an earthy variety 

 of dull gray, reddish and brownish, sometimes black, colors. It 

 may have been produced at any time since the deposition of the 

 rocks ; and it is beyond doubt now in progress at some places in 

 the State. 



The salt of the rocks is found only in solution in waters issuing 

 from the strata. At the present salt-works of Salina and Syracuse 

 the brine is obtained by borings. The wells are 150 to 310 feet deep 

 at the former place, and between 255 and 340 at the latter. 35 to 

 45 gallons of the water afford a bushel of salt ; while it takes 350 

 gallons of sea-water for the same result. 



