THEIR DISTRIBUTION AND CONFIGURATION. 585 



The principal chains throw out branches, and by mountain knots, as 

 they are called, unite with other secondary chains the whole com- 

 posing a mountain system; but the apparent irregularities of these 

 systems may always be referred to one common direction. 



If from the disposition of mountains we pass to their distribution, 

 we perceive that all chains which have sprung from the same geolo- 

 gical convulsion are always distinctly parallel, and the successive 

 chains distinctly perpendicular among themselves ; so that the age of 

 a chain is known by its direction. Nor is there anything to astonish 

 us in this species of symmetry, when we recollect that every sub- 

 stance previously liquefied or diluted by heat, and which, while cooling, 

 becomes contracted by the closer compression of its atoms, splits 

 with a certain degree of regularity, generally following lines which 

 intersect each other at right angles. And it is through the crevices 

 of the cooled terrestrial crust that these fused matters have escaped, 

 according to the hypothesis generally admitted by geologists, which, 

 by solidifying in their turn, have created the mountains. I can only 

 indicate these considerations to the reader ; their development would 

 beguile us too far from our prescribed path. 



If we direct our attention now to the configuration of mountains, 

 we shall see that this configuration depends essentially on the nature 

 of the rooks which constitute them. Granite, for example, is one of 

 those which offers the most varied outlines, as the reader may see 

 without quitting the United Kingdom, in the rugged, fantastic, broken 

 masses of the Argyllshire Highlands, that hem in the waters of Loch 

 Goil and Loch Long. Granite abounds in the tropical zone, and 

 seems to prefer chains of moderate elevation. Granite heights are 

 generally distinguished by abrupt and polished flanks, pointed or 

 dentelated summits, scarped approaches, deeply fissured slopes, and 

 narrow, wild, and profound valleys. 



Gneiss, a felspathic and micaceous rock, of schistous structure, is 

 found in layers sometimes horizontal or gently inclined, sometimes 

 undulating and complicated towards the border. The contours of 

 the gneiss mountains are less cloven than those of mountains of 



