146 



GEOLOGY OF EASTERN "WISCONSIN. 



The source of the substances found in these springs is cpite clear. 

 The salts of lime, magnesia, silica, alumina and ii-on, are the rock 

 substance dissolved, these being the essential constituents of the 

 strata from which the waters flow or through which they have per- 

 colated. It is to be noted that the relative proportions of these sub- 

 stances in the analyses bear a close correspondence to that which they 

 sustain in the rock. The compounds of sodium and potassium arc 

 for the most part those found in sea waters, whence they were de- 

 rived at the time of the deposition of the formations beneath the Si- 

 lurian ocean. The leaching of ages has not sufficed to completely 

 remove them from the interior of the strata, and these analyses show 

 -that they are still being dissolved out and borne back to the ocean. 

 The iodine which distinguishes the Beloit springs is doubtless derived 

 from the ancient sea weed that is imbedded in abundance in the rock 

 from wliich its flow is derived. It is true, iodine exists in sea water, 

 but in a much less proportion than bromine, while here it is greater. 

 It is further to be noticed that the ratio of iodide of sodium to chlo- 

 ride of sodium, the common salt of the ocean, is greater than in sea 

 water. These facts warrant the belief that the trace of bromine was 

 entrapped by the forming rocks in the same manner as the more com- 

 mon salts, but that the iodine arises from the sea weed that was 

 buried by the accumulating sediments. The proportion of iodide of 

 sodium to chloride of sodium — ^ common salt — is greater, with one 

 exception, than that found in twenty- two other springs containing 

 iodine, with which it was compared. 



