GEOLOGY OF SOIL. 17 



Jy determined without observations on the mean 

 temperature of the days which elapse between sow- 

 ing and harvest, and to this point the philosophic 

 farmer should direct his attention. In our country, 

 the isotheral line of 57-4 degrees, starting from Lab- 

 radore, 51 degrees, and passing between Hudson's 

 Bay and Lakes Superior and Huron, 50 degrees, 

 then turning north it approaches 58 degrees. At 

 Cumberland House, 54 degrees north, Capt. Frank- 

 lin found fields of barley, wheat, Indian corn. The 

 line approaching the Pacific ocean turns more south- 

 erly to compensate the increasing humidity. As 

 the limits of barley mark the boundary between the 

 races of shepherds, and hunters and fishers, and thus 

 presents itself in a moral view, so the limit of wheat 

 becomes interesting from coinciding in some parts 

 with that of fruit trees, as apples and pears, and 

 also with that of the oak. The whole aspect not 

 only of agriculture, but also of the orchard and for- 

 est changes at once on approaching the isotheral line 

 of 57*4 degrees, the northern limit of wheat. It 

 would be easy to extend these remarks to rye, still 

 the staple food of a large part of the population of 

 Europe, and to oats, little used for food for man out 

 of the "land o' cakes," yet growing in Norway, 

 as high as latitude 65 degrees. Each of these grains 

 2* 



