144 KatufaUUiitorical Collections, 



lava \vhich have flowed through the existing valleys, but also through solid rocks 

 of subjacent gneiss. They ftjrther prove, oh evidence which to me seems not short 

 of demonstration, that no great denuding wave or mass of water, lifted by super- 

 natural force above its ordinary level, could have assisted in forming such denu- 

 dations ; for the country is still studded with domes of incoherent matter, the 

 remnants of former craters ; from which may be traced, continuously, streams of 

 bva, intersected in the courses of the rivers by these deep gorges — the gages and 

 tests of the erosive power of running water during times comparatively recent. 



Hie elaborate Paper of Mr. Conybeare on the valley of the Thames is still 

 fresh in our recollection. He proves that the erosive power of the river has, within 

 the records of history, produced no effect on the general features of the country 

 through which it flows, and that the propelling force of its waters is not now, and 

 never could have been, adequate to the transport of the boulders which lie scat, 

 tered on the sides and summits of the chains of hills through which it has found 

 a passage : that much of the waterworn gravel, which has been drifted through 

 the breaches opened in the sinuous line of its channel, is composed of rocks not 

 found within the limits of its basin ; and that the form of the country is often 

 the very reverse of that which would have been produced by mere fluviatile ero-, 

 sion, however long continued. Similar facts are supplied by nearly all the greater 

 valleys of England ; and on the whole they point to one conclusion, that fluviatile 

 erosion, as a mere solitary agent, has produced but small efliects in modifying the 

 prominent features of our island : at the same time they leave untouched all the 

 facts of an opposite kind, supported by direct evidence, whether derived from the 

 volcanic districts of Central France, or from any other physical region on the sur- 

 face of the earth. 



The power of mountain torrents in transporting heavy masses of stone is strik- 

 ingly illustrated in a short paper by Mr. CuUey. He states that a small rivulet^ 

 descending from the Cheviot HiUs along a moderate declivity, carried down, dur- 

 ing a single flood, many thousand tons of gravel into the plains below ; and that 

 several blocks, from one-half to three-quarters of a ton weight each, were propelled 

 two miles in tlie direction of the stream. Facts, similar in kind, but on a scale 

 incomparably greater, must be in the recollection of every one who has seen tlie 

 Alpine torrents descending into the plains of the north of Italy. 



When mountain chains abut in the sea, the laws of degradation are not sus- 

 pended. At each successive flood, fragments of rock are drifted in the direction 

 of the descending torrents, and roUed beneath the waters. This kind of action 

 is, indeed, casual and interrupted ; but it is aided by another action which is lia- 

 ble to no intermission — the beating of the surf and the grinding of the tidal cur- 

 rents on all the projecting parts of a steep and rocky shore. Under such condi- 

 tions, I doubt not that there are now forming at the bottom of the sea, and at 

 depths perhaps inaccessible, alternating masses of silt, and sand, and gravel, 

 wliich, if ever lifted above the waters, may rival in magnitude some of the conglo- 

 merates of our older formations. 



Our last paper, on the excavating power of rivers, was from the pen of Mr. 

 Scrope. He contends that diluvial torrents would only form trough-shaped chan- 

 nels, extending in the direction of the principal rush of water ; .but would never 

 produce curves in which the excavating force worked in a direction opposed to that 

 of the general current. He describes part of the course of the Moselle and of the 

 Meuse, where the rivers wind through hard transition rocks, in long sinuous 

 channels, varying in depth from 500 to 1000 feet. In one of the great flexures 

 of the Moselle, the river, after passing over no less than 17 miles, returns to within . 

 500 yards of the point from which it started. These phenomena are regarded by 

 the author as sure indications of slow fluviatile erosion. For he considers the idea 

 of a great debacle, or diluvial current, winding its way back in lazy flexures to- 

 wards the point from which it started, as absolutely unintelligible. 



If I might give my own opinion on this debated question, I should say, that 

 the existing river drainage of our j)hysical region, is a complex result, depending 

 ugo» maoy conditions— the time when the region first became dry land — its ex- 



