74 



PKOCEEDIlSrGS OP THE GEOLOGICAL SOCIETY. 



dation than can be obtained from natural sections in brooks, where 

 the different gravels are moved and mixed up together by the recent 

 action of water. The total thickness of the gravel is 18 feet. 



Fig. 8. — Section showing Coal-seams squeezed into drift during the 



deposition of the lowest gravel on Hirwain Common. — Natural 



scale. 

 w. 



Bacon Hole, Gower, S. "Wales. 



Near this well-known cave limestone-gravel lies on a very steep 

 cliff of limestone, in some places sloping as much as 70° to the sea. 

 The top surface of this gravel lies at an angle of 34° ; and the 

 bottom fills up the concavity in the limestone rocks. The path to 

 the cave passes over this gravel, which is entirely composed of sharp 

 angular fragments of limestone, cemented together by carbonate of 

 lime, a process which seems to have been common in the Quaternary 

 period. I noted, on a previous occasion, the manner in which lime- 

 stone-blocks had been observed by Mr. Pengelly to be cemented 

 together near Torquay, at a considerable height above the sea. 



The mass of limestone-gravel falling down this cliff, accumu- 

 lating in concavities, and sloping to the sea at an angle of 32° S. 

 on the surface, may be seen at a height of 120 feet above the sea. 

 In its course from the high cliffs above, it seems to have sent off a 

 vein of gravel at a point 70 feet above the sea, to the east, at an 

 angle of 11°. 



This vein of angular gravel thickens to the east, and expands to a 

 thickness of 25 feet when it reaches the opening in the limestone 

 cliff called Bacon Hole, a deep fissure penetrating a long distance 

 into the limestone cliff, in a northerly direction, and having a roof 

 with an acute angle, which has often been described. 



