326 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuilG 5, 



Any one not prepared to find a curving-back on such a scale, might 

 easily mistake the superficial dip for the real dip. I confess I was 

 at first disposed to look on the dip as the result of a fault in the 

 adjacent valley, or as a part of a denuded or truncated anticlinal 

 fold ; but further inspection convinced me that it was only an ex- 

 aggerated continuation of the general curving-back above described; 

 and this conclusion was corroborated by Mr. Morgans, who is familiar, 

 from daily experience, with the internal structure of the district. 



6. Concluding HemarJcs. — I think all will admit that the sections 

 to which attention has been directed present indications of a cause 

 to which the term " stupendous" may be justly applied. Was it a 

 southerly progression of a crust of land-ice filling up the basin of 

 the Bristol Channel, and levelling the area between the Black 

 Mountains of Wales and the Exmoor tableland ? Was it a grounded 

 iceberg ? or floating ice in any other form * ? Was it a swift 

 oceanic current exerting a pressure on the underlying slates by 

 means of a forcible drifting forward of detritus ? Or was it a still 

 more violent rush of waters caused by a sudden upheaval or de- 

 pression of the land t ? 



Postscript. — Since writing the above, I have seen other instances 

 of the curving-back of slaty laminae. Within half a mile of Union 

 Street, Plymouth, in a cutting of the Exeter and South Devon Rail- 

 way, the edges of the slates are slightly but uniformly curved on 

 nearly level ground, in a southerly direction, or in the direction of the 

 cleavage-dip. On the left-hand side of th e road leading from Torquay 

 to Bishopstowe and St. Mary's Church, and at no great distance from 

 the Torquay Post Office, an artificial excavation (April 15th, 1867) 

 reveals an instance of terminal curvature on a rather extensive 

 scale ; and here, as in West Somerset, the line of demarcation be- 

 tween the undisturbed slate and the regular bed of curved laminae 

 is very distinctly marked. The direction, as in all the other in- 

 stances, is southerly, or nearly so, and the ground in that direction 

 is only very slightly inclined. I believe that in most parts of Devon, 

 West Somerset, and Cornwall, if not in other districts, where the 

 slates a,Te flexible, and where the cleavage-laminae dip at a consider- 

 able angle to the south, or where they are vertical with an approxi- 

 mately east and west strike, similar appearances might be disco- 

 vered, irrespective of the outline or inclination of the ground. It is 

 not difficult to conceive how the uniform curving-back would only 

 occur where the laminae leaned towards the moving agent (or at 

 least did not lean away from it), so as to offer a certain degree of 

 resistance to its action. In other places the planing- ofi* of the edges 



* See a notice of supposed ice-marks on the Mendip Hills by the author, in 

 the ' G-eologieal Magazine,' vol. iii. p. 574. 



t The Eev. Maxwell H, Close, in a very elaborate paper on the " Glaciation 

 of Ireland," read before the Eoyal Geological Society of Ireland, March 14, 1866, 

 and just published, has expressed his belief that the "broken and bent over" 

 edges of mica slate, in a quarry near Innishowen, cannot be explained by the 

 "weight of the hill," but are the result of a flow of land-ice. (See Journ. Eoy. 

 Geol. Soc. Ireland, vol. i. part 3. p. 207.) 



