AT THE FALLS OP NIAGARA. 355 



fixed air with an earthy calx. The rock on being rub- 

 bed or broken, emits a fetid or sulphureous odour; 

 evincing that it is a swine-stone or lapis suillus. This 

 disagreeable smell attends the limestone in this and the 

 adjacent regions. I possess pieces of it charged with 

 martial pyrites. And the sulphur, clay and iron of this 

 association, are intimately blended with the calcarious 

 carbonate. The existence of pyritical limestone ex- 

 plains how, by the decomposition of the pyrites, sulphuric 

 acid is produced, and gypsum formed. 



The calcarious nature of the upper rocks is evinced 

 by the fact, that in the neighbourhood of the great cata- 

 ract as well as at the whirlpool five miles down the river, 

 and at Queenstown, two miles further, the inhabitants 

 burn them into lime for economical purposes. But 

 the material is not always indeterminate or shapeless. 

 It assumes beautiful crystalline forms. Rhomboidal and 

 cubical crystals are formed on its surface, and in its cavi- 

 ties. The former are of a milkwhite colour, with ob- 

 lique angles. The latter are less frequent, generally 

 found in the same clusters with the others, of an almost 

 rectangular figure, and of a semi-transparent complexion. 

 Other crystals shoot along the vacuities of the limestone ; 

 some of an imperfect hexangular shape, and others in 

 clumps of acute six-sided crystals, both having a resem- 

 blance to the dog's-tooth-spar. All these are probably 

 modifications of the calcarious carbonate, by admixtures 

 of magnesia, iron, silex, and perhaps some other ingre- 

 dients. 



The layers of limestone are interspersed with small 

 masses or lumps of gypsum. This is generally of a 

 snowy whiteness, and indeterminate figure. But it is 

 sometimes finely semi-pellucid and lamellar. It is mis- 



