W. A. E. Ussher — Pleistocene Geology of Cornwall. 307 



V. — Pleistocene Geology of Cornwall. 1 



By W. A. E. Ussher, F.G.S. 



Part V. — Blown Sands and Eecent Marine. 



Notes on Blown Sands and Gravel Bars. 



Proceeding round the coast from Plymouth. 



1. Par. A low range of sand dunes separates the alluvial tracts 

 from the Par sands. 



2. Pentuan. A bank of coarse granitic sand, with bedding and 

 false bedding indicated by black bands of schorlaceous material, 

 dams off the sea from the low land at the mouth of Pentuan stream ; 

 on the landward mai'gin of the low tract a low range of sand dunes 

 has accumulated, apparently from the wind drift off the sand bank ; 

 the surface of the alluvium between them is strewn with similar 

 granitic sand. 



3 a. Falmouth. At the curve in the shore at Gyllyngvaes (Clay- 

 pole, Proc. Brist. Nat. Soc. Ser. 2, vol. v. p. 35) the top of the gravel 

 beach or bar coincides with the highest spring-tides. 



b. Swan Pool is dammed by a bar of small quartz pebbles, 80 

 yards broad, and in the highest part 5 feet above high-water. 



c. Mr. Godwin-Austen noticed (Eep. Brit. Assoc, for 1850, Trans, 

 of Sects, p. 71) a platform of bare rock near Falmouth, occupying 

 an intermediate position between high-water mark and the base of 

 the adjacent raised beach, which varies from 3 to 10 feet above it. 



d. Between Pennance Point and Maenporth, rock platforms occur 

 at about the level of spring-tide high-water, the traces of raised 

 beach in the vicinity being about 4 feet higher. 



e. South of Maenporth, rock reefs and platforms were noticed at 

 about 6 feet above ordinary high-water, the base of the adjacent 

 raised beach being 10 to 15 feet above that level. 



4. A strip of blown sand flanks the stream at Poljew ; at Gun- 

 walloe a considerable accumulation of blown sand covers high land 

 between Castle Mount and Towan. On N.W. of Castle Mount, 

 owing to the exposed situation, no blown sand occurs. 



5. The Loo Pool is dammed by a bar of small quartz pebble 

 gravel and coarse sand, with occasional flint and slate materials : 

 coarse brown blown sand caps the low cliffs to the south of it. 



6 a. Penzance. 



Dr. Boase (T.B.G.S. Corn. vol. iii. p. 131) gives a section of the 

 West Green sand bank, between Penzance and Newlyn, as follows : — ■ 



1. Granitic sand, of quartz, mica, hornblende slates with a little tin 



ore; quartz predominating 10 feet. 



2. Gravel, of hornblende slate pebbles from 1 to 3 inches in diameter, 



16 feet thick, resting on a submerged forest. 



He points out the difference between the present sea sand and 

 that forming the Green sand banks, between Marazion and Penzance 

 and Newlyn ; the former being finer, and composed of pulverized 

 clay-slate and elvan, whilst the latter appears to have been derived 



1 Concluded from the June Number, p. 263. 



