56 
PHYSICAL GEOGRAPHY. 
traverses our own continent. Mountains and hilly 
ranges are not unfrequently parallel to each other ; 
and, when viewed on the great scale, they often en- 
close vast tracts of country* within an irregularly 
curved area. With respect to the shape of hills or 
mountains, it is worthy of remark, that both sides 
do not have the same degree of inclination : on one 
side we generally find an abrupt escarpment, and 
on the other a gradual slope ; so that the general 
profile of any range, taken across the line of its di- 
rection, would present the figure of a ridge-like 
mass or a series of wedge-like masses ; a circum- 
stance occasioned, in great measure, by peculiari- 
ties of internal structure. It is a rare thing, more- 
over, for mountains or hills to form isolated and 
unconnected masses ; but, as already remarked, 
they occur in ranges or chains, having a definite 
direction, a considerable length, and a narrower, 
but still considerable breadth. Smaller spurs or 
branches are often thrown off into the surrounding 
country, which again may have their minor branch- 
es connected with them, the whole forming a regu- 
lar and continuous system of valleys. 
* Burr's Practical Geology, 
