ON THE ORIGIN OF MOUNTAINS. 



lines. Such are the Chalk Downs and the Cotteswold Hills. In these 

 respects they differ from our mountains, which are mostly arranged in 

 groups of partially isolated masses, rising here and there in peaks, 

 sometimes appearing with rugged or serrated outlines, at others in 

 rounded backs. The Pennine range, on the other hand, is an escarp- 

 ment of hills, which finally culminates in the so-called mountains of 

 Ingleboro' and Penyghent. Here we have the gradation in height 

 from one to the other ; and, indeed, if such elevated tracts were of 

 gradual formation we must expect evidence of passage from hill to 

 mountain. In point of structure the Pennine range is even and 

 regular, whereas the Lake Mountains are highly disturbed ; facts 

 which sufficiently account for their different aspect. But just as 

 mentally we distinguish between pond and lake, so may we form a 

 general distinction between hill and mountain, in looking at the broad 

 outlines of our scenery. 



The distinctive features whether of mountains or hills are 

 dependent upon their stony composition, the amount of disturbance 

 to which the rocks composing them have been subjected, the geological 

 age of these rocks (time in most cases meaning hardness,) and lastly, 

 upon denudation or sculpture. These factors are all important, though 

 least so is the antiquity of the rocks, which may vary very considerably. 



We have spoken of the composition, structure, age, and sculpture 

 of mountains. Into their composition many rocks enter, such as 

 granite and numerous igneous rocks, slate and limestone, sandstone 

 and conglomerate. We could not expect to see a mountain of clay, 

 sand, or gravel, although occasional fringes of such materials may be 

 found at different elevations ; but the rocks just mentioned include 

 hardened varieties of these. Such rocks belong to all times. Slates, 

 limestones, sandstones, and conglomerates, originally laid down under 

 water, in tolerably regular layers, occur in a very disturbed manner in 

 nearly all mountain ranges that have been carefully examined. In 

 regard to structure, the component rocks of mountains are generally 

 folded and contorted, and sometimes inverted, while eruptive or 

 igneous rocks intrude among them, and granitic rocks sometimes 

 appear as a central nucleus that has burst through and disturbed the 

 rocks that overlie it. 



Igneous rocks, which may have existed in a molten state long 

 previously to their eruption, are yet classified according to the geological 

 date when they were intruded among overlying rocks ; hence the 

 central nucleus of a mountain may be much newer than the overlying 

 rocks. The age of a mountain is decided by the age of the disturbance 

 which last affected the rocks which form essential portions of its mass. 

 Thus the mountains of Cumberland, Wales, and Scotland rank among 

 the oldest in the world. The Wrekin, in Shropshire, is, according to 

 the observations of Dr. Callaway, one of the very oldest in our country. 

 All these elevations reach a far higher antiquity than the 

 Himalayas or Andes, because the mass of those vast ranges is com- 

 posed of rock* much newer than our mountain strata. Professor 



