70 Upjield Green ct- C. D. Sherborn — • ^ 



upheaval, and consequently the existence of Chalk Rock in its normal 

 aspect implies the previous formation of some equivalent of the 

 T. lata zone. 



That the zone of IT. planus should be followed by that of 

 If. cortestudinarium is only natural, and if a larger number of the 

 pebbles were examined fragments of some of the rocky beds of this 

 zone might perhaps be more certainly recognized. In those which do 

 appear to belong to this zone it is interesting to find that remains of 

 Polyzoa are again a conspicuous feature. 



It is to be hoped that tlie Marine Biological Association will 

 continue the work of exploring the floor of the Channel and will 

 recover pebbles from positions still farther south and west, for it can 

 hardly be doubted that they have a wider distribution in those 

 directions than has yet been ascertained. Actual evidence of this 

 and farther investigation of the flints and cherts would be very 

 desii'able. 



IV. — On the Grnkrat, Geological Strxjctctre of \Vf-;stern Cornwa.ll, 

 WITH A Note on the Porthlujnet-Dodman Suction. 



By Upfield Green and C. Da vies Sherborn. 



jS^ attempting an explanation of the structure of Western Cornwall 



1 



it seems fairly evident that the first step should be a study of the 

 coast sections, for the interior of the countiy is so folded and buckled 

 that it is quite bewildering in its complexity. The natural sections 

 most useful for this purpose are those of Black Head to Gorran Haven, 

 St. Michael Carhayes to the Dodman, Falmouth to the Manacles, and 

 Trewavas to Mullion, since all these sections cross the lines of strike 

 more or less at right angles. It soon becomes abundantly clear that 

 the complexity of folding exhibited by the rocks is but the detail 

 of greater movements and need not seriously detain us. In 1908 

 Hpfield Green expressed our views on those greater movements in 

 the ninety-fifth report of the Trans. Roy. Geol. Soc. Cornwall, and 

 endeavoured to show that the great Hercynian movements had 

 involved Cornwall, throwing the country into three east and west 

 anticlinals with sinuous outcrops, which anticlinals had gradually 

 been forced over to the north into overfolds. These folds have been 

 further complicated, distorted, and confused by local minor bucklings 

 shown by the strata on every side. In the paper quoted a map was 

 given showing tlie major anticlinals, and one section across the 

 country from Newquay to PorthoUand was added to explain our 

 views on the subsequent overfolding of these anticlinals to the north. 

 In December, 1912, we jointly published a note on the Trewavas- 

 MuUion section, which we had Avritten in May, 1910, ami this second 

 section corresponded in a striking manner with our first from Newquay 

 to PorthoUand. 



For the purpose of clearing up our views on Cornwall it is necessary 

 to publish a third section, that from Porthluney to the Dodman, for 

 this fits on to the southern end of Green's Newquay to PorthoUand 

 section, and completes it for 2^ miles further south. 



