48 INTEKXAL HEAT OF THE EARTH. 



in an insular manner. It is quite independent, generally 

 speaking, of the limits of vegetation and of the presence of 

 high trees. 



The gradual acquirement of a true general or cosmical 

 view of the thermal relations of the crust of the earth in 

 the northern parts of the old continent, is an important 

 step in the progress of knowledge, as is the recognition that 

 the limit of the ground-ice, as well as the limits of particular 

 mean annual temperatures, and of the growth of trees, are 

 found in very different latitudes in different meridians, a 

 fact which must occasion the production of perpetual thermal 

 currents in the interior of the earth. In the north-west 

 of America, Franklin found the ground frozen in the 

 middle of August, at a depth of 1 7 inches. At a more 

 easterly part of the coast, in 71 12' latitude, Eichardson 

 saw in July the ice-stratum thawed as far down as three feet 

 below the herb-covered surface. It is to be desired that 

 scientific travellers may soon obtain for us a more general 

 knowledge of the geothermic relations subsisting in this part 

 of the world and in the southern hemisphere. Eesearch 

 into the connection of phenomena leads us most surely to 

 the recognition of the causes of apparently complex or 

 anomalous facts, or of what is sometimes too hastily called 

 irregulanty. 



