272 Notes upon the Diluvial and Alluvial Deposits of the Taffe Valley. 



height ; are we to suppose, which seems the most probable hypothesis, 

 that at one time the horizontal formations extended to a higher level than 

 they do at present, and that the forces by which the present ineqiuilities 

 of the surface were modelled, have swept away the more exposed of their 

 upper strata? Under this hypothesis, the period of the dislocation would 

 have been subsequent to the deposition of the horizontal rocks, which, from 

 their upturned edges, seems certainly to have been the case. The period 

 of the convulsion by which the anticlinal line was formed, seems to have 

 occurred between the deposition of the inclined and horizontal rocks, the 

 latter not having been affected by it, and is therefore much older than the 

 fault.* 



It seems probable, from the appearances described, that the Point of 

 Portishead divides two coal fields, the one lying towards the north, and 

 covered up by the sea, and the other extending along the south-eastern 

 skirts of the hills, and covered up by the alluvion of the marsh. Unfortu- 

 nately, we have been unable to obtain a record of the results of the trial 

 made on a former occasion, near the mill ; and although it seems highly 

 probable that a trial for coal in any direction along the south-eastern 

 border of the Portishead hills would be successful, it may justly admit of a 

 question as to the probable thickness of the seams, and the practicability 

 of working them profitably at a nearly vertical dip. 



The present report differs in some respects with regard to the direction 

 of the fault, anticlinal, &c. from that referred to as published by Messrs. 

 Conybeare and Buckland. These differences may perhaps be accounted 

 for by the enlarged scale of the present map. In alluding to the labours 

 of these gentlemen, it is but due to them to acknowledge the general as- 

 sistance which they have afforded us, and to bear a willing, though un- 

 necessary, testimony to the general accuracy of their observation?. 



* Such of our readers as are in any degree conversant with the Geology of the 

 Clapton district, are aware, that the rocks on the north side of the ahove fault have 

 been brought, by the convulsion that produced the great Clapton fault, from the 

 ridge of Naish House, a distance of two miles ; and that the line of fault, extending 

 from near Naish House to Portishead Battery, is in truth the arc through which the 

 ridge of Walton, Weston, and Portishead Downs has been wheeled. For a clear and 

 masterly explication of the phjenomena produced by this convulsion, the reader is 

 referred to the paper on the South-Western Coal District of England, drawn up by 

 Messrs. Conybeare and Buckland, and printed in the Geological Transactions for 1824. 



SHORT NOTES UPON THE DILUVIAL AND ALLUVIAL 

 DEPOSITS OF THE TAFFE VALLEY. 



TuE river Taffe occupies a long and somewhat confined valley, extending 

 from Merthyr Tydvil on the north, to the ravine of Castel Coch on the 

 south, when it suddenly expands into a comparatively level plain, across 

 which the river winds to the Bristol Channel. 



