8 THE GEOLOGY OF TYTHEEINGTON AND GKOVESEND. 



beyond the tunnel mouth. They dip somewhat irregularly 

 from 16° to 25° S. by E. to S.S.E. And since the line of 

 rails in the tunnel runs nearly east and west (5° N. of W. 

 and 5° S. of E.), this part of the section runs nearly, but 

 not quite, along the strike of the beds. As seen in the sec- 

 tion, the thin bands of limestone are thrown into slightly 

 waving folds ; similar folds are noted by Mr. Winwood as 

 occurring in the tunnel. 



The limestones are, for the most part, thinly-bedded, close- 

 grained, and argillaceous, mottled or streaked with green, 

 pink, and purple. Between them are partings of red, pink, 

 and grey shales. We measured 118 feet of these beds before 

 the tunnel mouth. 



At the other end of the tunnel, shales and fine-grained 

 argillaceous limestone, weathering white, are seen overlying 

 very dense and solid oolitic limestones. 



I believe the shales and argillaceous limestones here seen 

 form a continuous series with those on the other side of 

 the tunnel. It is impossible to estimate with accuracy the 

 thickness of beds hidden by the tunnel. But seeing how 

 nearly it runs along the strike of the strata, I cannot think 

 that there are more than 20 or 30 feet. I am convinced 

 that Mr. Winwood is in error in assigning a thickness of 

 178 feet to the beds hidden by the tunnel. 



I estimate the total thickness of the beds above the oolitic 

 limestone in this sub-section at 150 to 160 feet. 



Just beyond the tunnel mouth the cutting is, on the south 

 side, walled up. This wall covers the entrance to a great 

 cavern, or underground watercourse, which dipped down 

 southwards, and ran for a distance of two or three hundred 

 feet. A small hollow, about 7 feet deep by 3^ wide, has 

 recently been holed into on the north side of the line; 

 and a somewhat larger cavity, 20 or 25 feet long, has been 



