GEOLOGY OF SOIL. 13 



2d. The equatorial limits, bylines of equal winter 

 heat. 



These lines are called respectively, isotheral, and 

 isochimenal. They by no means coincide. They 

 often cut each other at right angles, and generally, 

 from about 45° north latitude, they are parallel 

 neither to one another, nor to the latitude. They 

 are often highly curved. 



And now for the proof of these general laws — be- 

 ginning with barley, the grass or grain which has 

 been cultivated the farthest north. Its fields are 

 found in the extremity of Scotland, in tht Orkneys 

 and Shetland Isles, 61° N.; in the Ferue Islands, 

 61° — 62° 1-2 N.; in Western Lapland, near North 

 Cape, in latitude 70° ; on the borders of the 

 White Sea, in Western Russia, between 67° and 

 68°, and near to Archangel, in Eastern Ruria. about 

 66°. in Central Siberia, the limit of bailey is be- 

 tween 58° and 59° N. There are no extended ob- 

 servations of the temperature of the northern portions 

 of our own continent, and therefore the limit of 

 barley in Northern America is left undefined. But 

 its European line will probably define that which 

 will limit grain cultivation in America. 



Tracing a line through the points above named, it 

 is the northern boundary of all the cereals, or grains. 



