OCR Text |
Show 234 VALLEYS AND RASINS. to Shrewsbury, or that of the Dee from Bala to Wynnestay, to say nothing of the lower part of either, and it will be found much nearer to the truth to say that the valley is the cause of the river, than that the river is the cause of the valley. If the lower parts of the valleys were taken, the accumulation of debris might perhaps be accounted for; but what could the Severn do towards the hewing out of the Wrekin, or the Dee to that of Beeston rock 1 In places which have more of an alpine character, the formation of the valley by the river, even though that river had been running for a million of years, would be, if possible, still more puzzling. The Ty~e and the Tiviot never could have excavated theu dales; and even if they had, what stream paused on its course, and altered the whole system of its workin< T. in order to find basins for "the lakes 1" The T~y and Its branches may have cut through a pass or two, at Dunkeld, Killiecrankie, and some other places; but to suppose that any of the valleys was alto<Tether formed by the action of the stream is an abs;rd1:ty. The most conclusive instance (if any can be more conclusive than another, in a case where the very simplest affords demonstration) is the great valley of the Scotch Highlands, from th& Moray Firth on the east, to Loch Linnhe on the west. There is a little dike of stone, which crosses that valley somewhere near the midway between the two seas; but much of the rest is in alluvial formations, and in the basins of lakes absolutely lower than the bottom of the adjoining sea, to which the Ness, the largest river of that singular valley, runs. Nor are the proofs confined to the mere forms of surfaces, for they are to be found in the very rocks themselves. Where the schistose, or stratified rocks meet the granular ones, they are twisted and bent in all directions, as they would have been had they been upheaved by some action from below; and at many of the lines of junction one of the rocks is melted as if ) FORMATION OF ROCKS. 235 the other had come to it in a state , of i<Tnition · and we know of no action from above eve~ if w~ suppose a dei?ositation from any imaginable depth of water, which could have given the plrtes' or strata, the inclinations which we observe. In a b~sin of coal strata, or any of those that have a hollow of which we can obtain the section, so that th~ ~eve~allayers "crop out" all round, we can perhaps ~ma&me how they may ha_ve been formed by successive growths and depos1tes above. But even in those, ~he coal, which is vegetable matter, ~nd matter which must have grown, not in the sea, or in any oth~r way ~nder water,. but in the air on dry land, as It contams the remams of land productions often lies under other f~rma~i~ns, which must just as clearly have had theu ongm, not merely in the sea, but in deep water. The granular rocks, which have no appearance of ~lates, ~r strata, but arc great lumps, and lumps havmg thmr upper surfaces very much re~embling what we would expect from matter forced up from beneath, ar~ perhaps the most striking proofs that the ~ount~ms and valleys of which the principal part Is native stone have been elevated from under water. In the mo~n~ains of gr.anite and porphyry, the:e are also precipices and cliffs, the formation of which cannot be attributed to any known cause that can act above the level of the sea. That cannot have been produced by the action of water that has fallen in rain, or in any way run in streams· because there i~ not only now no water at all equ~l to the producmg ~f the effect which we see, but there is no channelm which .water could ~t any time have run. Many of our highest moun tams-those which over~o.p all. the country round-have horse-shoe P!eciptces m their sides (often in the north-east SI~e)., the tops of which are higher than any thing Withm many miles; and therefore we cannot suppose them to have been formed by the action of |