Vol. 60.] AN EOCENE OUTLIER OFF THE CORNISH COAST. 1-13 



9. On the probable Occurrence of an Eocene Outlier off the 

 Cornish Coast. By Clement Reid, Esq., F.K.S., F.L.S., F.G.S. 

 (Read March 9th, 1904). 1 



During the new geological survey of the Hampshire Basin fresh 

 evidence was discovered of the westerly extension of certain of the 

 deposits, in the form of Eocene river-gravels. 2 This evidence tended 

 to link more closely the Eocene deposits of Devon with those of 

 the Hampshire Basin ; but it did not seem to throw any light 

 on the Eocene geology of Cornwall, nor of any part of the area 

 west of Dartmoor. 



Some years since (in 1897) during a holiday-visit to the Lizard, 

 I was much impressed by the character of the material which forms 

 the extensive shingle-beach at Gunwalloe, on the western side of the 

 Lizard promontory, not far from Mullion. The shingle, which was 

 being extensively carted away for gravel, was so perfectly rounded, 

 and in appearance was so unlike anything that I had expected to 

 find in Cornwall, that I examined it closely, taking away samples 

 to give to the Museum of Practical Geology, Jermyn Street. The 

 coarser beach proved to consist largely (about 70 per cent, by weight) 

 of Chalk-flint and Greensand-chert, only 30 per cent, being Palaeozoic 

 at the spot where it was examined. A large quantity of the fine 

 shingle yielded : — 



per cent. 



Chalk-flint 86"0 



Greensand-chert 20 



Quartz 90 



Grit 2-5 



Serpentine 0*5 



1000 



At the time, I was unable to carry the matter further ; for, 

 although well aware that scattered Chalk-flints were not uncommon 

 in Cornwall, I could not understand why so many had collected at 

 this spot, almost to the exclusion of the local rocks. The absence 

 of Chalk-flints from the Pliocene gravels of St. Erth seemed to 

 suggest that the Mullion gravel might be a Pleistocene deposit of 

 glacial origin, or derived from some such deposit. 



In 1901 and 1903, during the completion of the maps bordering 

 on Mount's Bay for the Geological Survey, an opportunity was 

 given for an examination of the deposits of Chalk-flint which are 

 known to occur in the neighbourhood of Penzance, especially in 



1 Communicated by permission of the Director of H.M. Geological Survey. 



2 'The Eocene Deposits of Dorset' Quart. Journ. Geol. Soc. vol. lii (1896) 

 pp. 490-95 ; & ' The Eocene Deposits of Devon ' ibid. vol. liv (1898) pp. 234-36. 



Q.J.G.S. No. 238. i 



