92 Essay on Geology. 



generally tbrown up at a very high angle, and often nearly vertical : and 

 it is traversed by precipitous ravines of the very boldest character, so that 

 we cannot desire a better opportunity of studying the phaenomena of ele- 

 vation, or examining the rents which appear to have been occasioned by 

 these disturbing forces. The features of Cheddar Clifts are not often ex- 

 ceeded in magnificence, even in far more mountainous countries. If we 

 carry our eyes from south-west towards the north-west, we still observe 

 detached hills of the same carboniferous limestone, combining to form the 

 boundary of the great coal basin (as such depressions of the strata are 

 technically termed) of North Somerset and South Gloucester. The first of 

 these, Broadfield Down, abounds, like the Mendips, in fine ravines. 

 Brockley and Cleeve Combes will equally repay the geologist or artist who 

 may visit them. The features of the nearer ranges of Leigh and Durdham 

 Downs must be familiar to every Bristolian ; and every one must be well 

 acquainted with the abrupt defile opening between them, as it were, on 

 purpose to afibrd an outlet to the Avon, which, were this breach closed, 

 would cover all Bristol, except St. Michael's hill, and all the low grounds 

 between this and the Kingswood hills, and convert them into an extended 

 lake. This defile is no less geologically interesting than picturesquely 

 beautiful, and presents very instructive examples of compound fractures, as 

 they may be called, of the rocks. We shall hope to give a full description 

 of this ravine in a future number, as it will afford our readers the most 

 illustrative geological walk, and that close to their own doors ; but the 

 subject would require graphic illustration, and for the present we must 

 content ourselves with saying, that it will be found to afford the best 

 examples of all that has been said in our general outline, with regard to 

 faults and dislocations. 



We should next call our observer's attention to the points in our 

 geological panorama connected with the history of the coal measures, or 

 strata immediately alternating with the coal. Behind the Hotwell House 

 will be seen a bed of shale, immediately reposing on the carboniferous lime- 

 stone, and containing tlie lowest trace of coal ; but it is a mere trace, and 

 is separated from the principal deposit by a thick mass of compact quart- 

 zose grit 5 this exhibits itself at Brandon Hill, and the hills above Ashton 

 Park. At the foot of these hills succeeds a great thickness of argillaceous 

 shale, containing the p. incipal coal seams j these are very generally covered 

 np in our district by more recent and nearly horizontal overlying deposits, 

 as they are called, of red marl and lias j but the coal has been worked by 

 pits, sunk through this cover, as may be seen a little below our station, in 

 the Bedminster collieries. This argillaceous series is succeeded l)y a thick 

 deposit of coarse sandstone, abounding in specks of coal, and often present- 

 ing vegetable remains ; this sandstone rises into low hills, in the coal fields 

 of Kingswood and Coalpit Heath, which are separated from one another 

 by a great undulation of the strata, or anticlinal line. The ravine through 



