STRUCTURE OF MOUNTAINS. 351 



argue upon that level as a general standard to which we may refer all 

 the effects of internal movements, in whatever period, and by what- 

 ever forces produced. It fixes no limits to the effects of the temporary 

 violence induced in the ocean by such movements, because these effects 

 would be in proportion to the impulse with which they originate. 



Mountain Ranges. 



Study of Mountains. Long chains and insulated groups of moun- 

 tains form, so to speak, the skeleton of the earth, and are the funda- 

 mental features of its topography ; their insulated groups characterise 

 kingdoms, their long connected chains divide the races of mankind, 

 and define the geographical limits of the distribution of land animals. 

 The principal ranges of mountains everywhere contain in their axes 

 similar rocks, which are often the lowest, and among the oldest, 

 with which we are acquainted. By lateral contraction they have been 

 lifted to their present heights, so as to break through and rise by denu- 

 dation from beneath the strata which were superimposed upon them 

 in succession. 



These mountain-forming materials comprise gneiss, mica schist, 

 slate, and many associated rocks, resting upon and often pierced by 

 granite and similar crytallised compounds. 



Though we speak of long-continued chains and belts of mountains, 

 it is certain that to be crossed in groups is the real character of moun- 

 tain association, and that the chains and belts are nothing but ap- 

 proximated groups. A geological map is in this respect a most valu- 

 able instructor; from it we see that, instead of the plains being 

 commonly insulated among the mountains, the newer strata spread 

 wide, and round the bases of the mountains, as the ocean encircles 

 islands and continents. We may observe that the most insulated 

 and many of the loftiest eminences on the surface of the earth are 

 volcanic summits. The most connected ranges of uniformly high 

 ground are formed by limestones. 



Elie de Beaumont supposed that all ranges of mountains which 

 were uplifted at the same period are parallel to the same great circle 

 on the sphere. Parallel ranges are an effect that lateral pressure would 

 produce. 



If a great circle be conceived to pass round the earth through 

 Xatches and the mouth of the Persian Gulf, and the directions of 

 mountain chains be compared with it, it will appear that the Pyre- 

 nees, part of the Apennines, the Dalmatian and Croatian ranges, and 

 part of the Carpathians, are parallel to it. In accordance with the 

 researches of some geologists, M. de Beaumont supposed that all these 

 mountain chains were thrown up at the same geological epoch. 



Another circle may be traced on the sphere parallel to the Alps, 

 from the Valais to Styria, and to this system we may refer the Atlas, 

 the Caucasus, the Balkan, the Himalaya, &c. ; and, according to the 

 hypothesis of M. de Beaumont, these must have been all raised since 



