S. G. Williams — Gypsum Deposits in New York. 217 



and black laminated mud at the other, although elsewhere the 

 gypsum and mud were separated by irregular joint-like cracks. 

 I was inclined to attribute the change to the action of water 

 penetrating to the beds through crevices in the clay cover. 



The limestone of that part of the series in question which 

 encloses the gypsum beds is of a prevailing drab or ash color, 

 with a few blue seams, of which No. 2 of the section is the 

 only important one. It is often highly laminated ; has a con- 

 siderable amount of impurities as has already been said ; and 

 by reason of the earthy character of these impurities, it shows 

 such a disposition to absorb water as to unfit it for all but the 

 roughest purposes. A fragment of No. 1 gained in weight 3 

 per cent by two hours soaking, while a like fragment of the 

 blue limestone No. 2 showed no appreciable gain in the same 

 time. 



The character of the limestones just described seems to me 

 to throw light on the question of the origin of the gypsum bed' 7 ; 

 these I think have obviously been formed from the earthy 

 drab limestones of the horizon at which they occur, as the result 

 of the action upon them of acid waters originating in sulphur 

 springs, which are still somewhat abundant in this region, and 

 which it may be presumed were more abundant at an earlier 

 geological date. The porous character of the drab-colored 

 limestones would facilitate such a transformation, under favora- 

 ble circumstances; while the imperviousness of the blue lime- 

 stone which underlies the series would limit it below. Reasons 

 for this opinion as to origin may be found . first, in the strik- 

 ing similarity in structure between the lower gypsum and the 

 associated drab limestones, both having the same highly lam- 

 inated character, while both the lower gypsum and the northern 

 part of the upper, are also distinctly bedded ; second, in the 

 structure of the intermediate bed, containing as it does alternate 

 layers of gypsum and shale, as if whatever was lime in an im- 

 pure shaly limestone had been transformed to gypsum, leaving 

 the remainder unchanged ; third, in the presence in all the 

 gypsum beds of native sulphur which would be difficult to 

 account for on any theory of origin which should not include 

 the action of sulphuretted waters ; fourth, in the composition 

 of the gypsum itself, which is gray, and like the limestones 

 somewhat impure, containing in commercial samples an average 

 of 80-| per cent of lime sulphate, with 14 per cent of earthy 

 matter, 5 per cent of lime and magnesian carbonates, and, quite 

 significantly, .6 per cent of lime phosphate and organic matter, 

 these last ingredients suggesting an organic origin, while the 

 residual lime and magnesia point to the probable original con- 

 dition of the deposit. It may be added in this connection that 



Am. Jour. Sci.— Third Series, Vol. XXX, No. 177.— Sept., 1885. 

 14 



