284 THE CANADIAN NATURALIST. [Aug. 



in other words, to a gradual elimination of iodine from the sea- 

 waters, and its fixation in the earth's crust. The observations of 

 numerous chemists unite to show the frequent occurence of small 

 portions of iodine in some unknown combination, in sedimentary 

 rocks of various kinds; from which we may conjecture that it was 

 in former times abstracted from the sea, either directly or through 

 the intervention of organic bodies (as in the case of potash, which 

 is separated and fixed by means of algae, § 5). Experiments after 

 the manner of those of Way and Voelcker may throw light upon this 

 interesting question. We are aware that insoluble combinations of 

 soluble chlorids with silicates of alumina are formed under certain 

 conditions, as appears in the generation of sodalite, eudyalite, and 

 the chloriferous micas, and it is not improbable that the soluble 

 iodids may give rise to similar compounds. By such a process 

 might be explained the rarity of this element in modern seas, 

 while the occasional re-solution of the iodine from these insoluble 

 compounds by infiltrating waters, would help to explain the 

 variable and often large proportions in which this element is met 

 with in some of the waters noticed above. 



§ 61. Sulphates. — In the preceding sections we have already 

 discussed the principal facts in the history of those neutral waters 

 in which sulphates predominate, or prevail to the exclusion of chlo- 

 rids (§ 50, 51.) The history and the probable origin of those curious 

 springs which contain free sulphuric acid has also been considered 

 (§ 31, 48, 49) ; and it now remains to notice the relation of sulph- 

 ates to the muriated waters. The first fact that excites our attention 

 is that of the total absence of sulphates from numerous springs of 

 the first, second and third classes ; as shown in the preceding analyses, 

 and also in the observations of Lenny and others on the saline 

 waters over a great area in western Pennsylvania (§ 40). 



The elimination of sulphate in the form of gypsum from evapo- 

 rating waters containing an excess of chloric! of calcium, has already 

 been discussed in § 37 ; but the bitterns resulting from such a pro- 

 cess still retain small portions of sulphates ; while it is to be re- 

 marked that the saline waters under consideration contain no traces 

 of sulphates, and in many instances hold portions of baryta and 

 strontia, bases incompatible with the presence of sulphates. The 

 modes in which this complete elimination of sulphates may be effected 

 are two in number. The first has already been suggested in § 10, 

 and depends upon the deoxydizing power of organic matters, which 

 reduce the sulphates to sulphurets. These in their turn may be 



