182 THE CANADIAN NATURALIST. [June 



nant element in mineral waters. In connection with a suggestion 

 made in the section last cited, it may be remarked that I have since 

 found that predazzite, in virtue of the hydrate of magnesia which 

 it contains, readily decomposes solutions of gypsum holding car- 

 bonic acid in solution, and gives rise to sulphate of magnesia. 



In the second place, sulphuric-acid waters, like those described 

 in § 47, by their action upon calcareous and magnesian rocks, or by 

 the intervention of carbonate of soda, may, as already suggested, 

 give rise to neutral sulphated waters of the sixth class. It is 

 evident also that waters impregnated with sulphates of alumina and 

 iron from oxydizing sulphates, as mentioned in § 28, may be de- 

 composed in a similar manner, and with like results. 



Neutral sulphated waters generated by any of the above pro- 

 cesses, are evidently subject to admixtures of saline maters from 

 other sources, and may thus become impregnated with chlorids 

 and carbonates. Indeed it is rare to find waters of the sixth 

 class without some portion of chlorids ; and a transition is thus 

 presented to the waters of the first four classes, in which also 

 portions of sulphates are of frequent occurrence. The presence of 

 sulphates being one of the conditions required for the generation 

 of sulphuretted hydrogen (§ 10), we find that the waters of the 

 sixth class are very often sulphurous. 



§ 51. Waters of the sixth class are very frequently met with 

 in the palaeozoic rocks of New York and western Canada, and are 

 probably derived from the gypsum which is found in greater 

 or less abundance at various horizons, from the Calciferous sand- 

 rock to the Onondaga salt-group. It is however not improbable 

 that the sulphuric-acid waters which abound in this region (§ 48) 

 may, by their neutralization, give rise to similar springs. In the 

 waters of the district under consideration, the sulphate of lime 

 generally predominates over the sulphates of the other bases, and 

 chlorids are frequently present in considerable quantities. For 

 numerous analyses of these waters, see Beck, Mineralogy of New 

 York. The results of an examination of the Charlotteville spring, 

 remarkable for the amount of sulphuretted hydrogen which it con- 

 tains, will be found in Silliman's Journal [2], viii, 369. A copious 

 sulptm- spring which issues from a mound of calcareous tufa in 

 Bra. /, C.W., overlying the Corniferous limestone, is distinguished 

 by the absence of any trace of chlorids ; in which respect it resem- 

 bles the acid waters of the fifth class from the adjacent region. 

 A partial analysis of a portion of it collected in 1861, gave for 



