ANNUAL REPORT FOR 1873. 33 



combination with chlorine. Epsom salt (sulphate of magnesia) is 

 found only in two; sulphate of lime is equally rare, being only found 

 in two cases. The very small amount of alumina is remarkable, 

 where there is so much clay in the soil. The occurrence of chloride 

 of lithium * and nitrate of soda is also an interesting variation in the 

 composition of these waters, being only found in the well at Water- 

 loo. Possibly the proximity of this locality to the quiirtzite (and 

 perhaps other Archaean rocks) may have something to do with this 

 variation. 



The absence of nitrogen, ammonia, the bromides, iodides, etc., will 

 be remarked by persons familiar with the composition of mineral 

 waters. 



In seeking for the cause of this unusual absence of mineral matter 

 in our spring waters, we must remember that the geological history 

 of Wisconsin differs essentially from that of other countries. A large 

 proportion of the state is underlaid by rocks of Archaean age, an age 

 the furtherest remote from the present, while the remainder is almost 

 exclusively occupied by Silurian rocks, they being the oldest of the 

 fossil bearing series. It thus appears that during all the ages of the 

 Carboniferous, Permian, Jurassic, Triassic, Cretaceous and Tertiary 

 periods, Wisconsin continued to be dry land, subject to the abrading, 

 and purifying action of rains and frost. This is still further attested 

 by the wonderful amount of denudation our strata have sustained, and 

 which it is made the duty of the survey to investigate. While the 

 Alleghany and Rocky mountains were being uplifted from the depths 

 of the sea, Wisconsin stood firm, always above its waters, always con- 

 tributing of her substance for the accumulation of the sedimentary 

 rocks of the adjoining states contributions which she still continues 

 to make. 



During all these vast periods, each occupying an incalculable length 

 of time, rains have continued to fall, the waters have continued to 

 percolate through the soil and porous rocks, dissolving and carrying 

 away all soluble substances. It is not therefore wonderful that by 

 this time the waters of the state have an unusual degree of purity. 

 Waters percolating through our limestones and sandstones can now 

 absorb but small amounts of earthy or alkaline salts. 



The waters now examined are chiefly from the southern and south- 

 eastern portions of the state, where the several magnesian limestones 

 prevail; and hence they contain, as before stated, as chief ingredients, 

 the carbonates of lime and magnesia, resulting directly from the de- 



* By a typographical error, the quantity of lithium in the Waterloo water has been 

 overstated; it is correctly given in the table above. 

 Wis. SUB. 3 



