4o6 Sources of the Constituents of Minnesota Soils. 



uses. The calcareous and siliceous shales spring from widely 

 divergent geologic periods and bring to the making of soils 

 somewhat different physical and chemical factors. Their influ- 

 ence is wholesome and strengthening. F'inally the carbonates 

 come before the eye in this chemical review. They yield, for 

 soil making, carbonic acid, lime, magnesia and small quantities of 

 other compounds. When the condition of a soil is reached, but 

 a small percentage of these rocks is left, but this is a substantial 

 part and enters into the constitution of the best soils of the state 

 They appear in full force in the southeastern corner of the state 

 where stands a portion of that old glacial island, a tract over 

 which the ice did not flow during the period when all the rest 

 of the state was buried deep beneath the glacier. 

 December 8, i8qi. 



