402 ANNUAL REPORT. 



through the soil and into the earth to be carried off in subterranean 

 streams; at all events it never appears in the discharge of the rivers 

 draining the state, according to the best of capacity measurements 

 thus far made. These streams carry away only a fraction over 

 twenty-four per cent., if the records of Humphrey and Abbott are 

 taken as a basis of estimate. While rainfall remains the same from 

 year to year the discharge through streams is becoming less. The 

 water which remains to work its way through the soil and under- 

 lying rocks, after taking solvents from the air, and additional sol- 

 vents in the way of acids and alkalies absorbed from the soil, has its 

 disintregating powers vastly increased. 



When we see the firm granites, schists and limestones crumbled 

 and transformed, as in the Minnesota and Mississippi valleys, there 

 can be no wonder thab this drift material with its bowlders, pebbles, 

 gravel, sand, marl and clay, in its porous condition, is being rapidly 

 pulverized and its lime, magnesia, potash, soda and ammonia in their 

 various compounds, making the sum total of plant food, are impart- 

 ing to the soil that variety of composition so essential to the best 

 results in a diversified agriculture. 



Where these subterranean streams formed beneath our state flow, 

 before they find their way to the universal ocean, is not for us to 

 know nor to speculate about at this time. Many of them appear 

 in springs so filled with mineral matter as to be hard or alkaline; 

 others have properties so pronounced that they are much prized for 

 their medicinal value. 



Springs of soft water are rare here; the reason for this is hinted 

 at above. 



The temperature of Minnesota is another subject of vital im- 

 portance to the agriculturist. Our 10,000 lakes form a vast res- 

 ervoir of heat of which a single computation may give a more 

 definite conception. According to Terry* the lakes will give an 

 average, taken at their highest temperature, of about 75°, or 43° 

 above freezing point. Ten feet may be taken as a fair average of 

 depth for the 5638 square miles of water surface, thus giving 10.68 

 cubic miles of water. Each cubic foot will contain about 1,250,000 

 loot pounds of heat, or heat enough to raise a weight of 1,250,000 

 pounds one foot from the earth, thus giving to the whole bulk of 

 water the enormous power of 1,962,639,360,000,000,000 pounds! 

 In other words there is heat enough stowed up in our Minnesota 

 lakes each summer and given off during the cooling autumn to 



*Ueol. and Nat, Hist. Sur. of Minn., 1880, p. 314, et seq. 



