44 SECTION FROM THE LAURENTIAN AXIS TO THE ROCKY MOUNTAINS. 
of pressure by overlying beds to which they have been subjected ; second, the greater 
alteration, accompanied by flexure, to which the rocks in the vicinity of the mountains 
have been subjected. The second is, however, found to be much more influential than 
the first. 
The belts of country characterized by different classes of fuels are indicated on the 
section. The eastern, over which the word Lignite appears, yields fuels which, though 
often containing little ash and well adapted for local use, hold generally more than 12 per 
cent. of hygroscopic water. The next, designated as that of Lignite Coals, frequently yields 
fuels containing less than 12 per cent. of water, and in some instances not half this amount, 
and also by their physical character better adapted for transport. The third, a narrow 
zone, co-extensive with that of great disturbance, affords fuels which contain little water, 
often give firm cokes on heating, yield abundance of highly luminous hydrocarbons, 
and are scarcely distinguishable from coals of the Carboniferous period proper. 
This change is analogous to that found in passing from the bituminous coals of the 
western shales to the anthracites of the disturbed Appalachian region to the east. 
