UPPER EOCENE (bARTON AND UPPER BAQSHOT FORMATIONS). 593 



series has been described in some detail by Tawney and Keeping*. 

 The zone of Oliva Branderl can be traced half a mile west of the 

 boundary ; but as soon as it overlaps the protecting clay above, it 

 becomes unfossiliferous. The underlying sand-bed also, in its turn, 

 loses its alum and plasticity and becomes loosened and carried away 

 by the wind as well as stained by the gravel as soon as it passes 

 beyond the limits of the clay. The Chama-hedi likewise becomes 

 altered by percolating water as soon as the dip brings it near to the 

 top of the section, and it is then undistinguishablo from the beds 

 above. The Upper Bartons continue in this state, in considerable 

 thickness under the gravels, to at least Barton Lane End, the curve 

 in the bay moderating the dip and causing them to maintain their 

 position for so great a distance f. 



Dr. Wright drew the line between his Lower Marine Formation 

 and Estuary Formation at this horizon ; but Prof. Prestwich in- 

 cluded the overlying 15 or 20 feet of sands with the Barton Beds, 

 because, where fossiliferous, as here and at Whitecliff Bay, they con- 

 tinue to contain Barton types. We entirely endorse this view, 

 believing it to be impossible to draw any line of division at this par- 

 ticular point, and greatly preferring to take the Lignite-band at the 

 base of the Lower Headon just above, as the limit of the Barton 

 Series. 



The Long-Mead-End Sands rest upon these, and we found their ver- 

 tical thickness to be 20 feet, and their angle 46°. The base is slightly 

 clayey, white sand, with mixed roundish and fractured grains, some 

 of which, as Mr. Cole observes, still show surfaces of conchoidal 

 fracture. The bed becomes purer and tawny for 15 feet and is 

 without fossils ; but towards the top shells become abundant, and 

 are drifted into pockets. Psammobia rudis is the first to appear, 

 followed by Cerithium concavum, Ancillaria perita, Oliva Bra7ideri, 

 Lucina gibhosida, Cyrena gibbosula, Melania fasciata, and remains 

 of large and small turtles. There is an uneven junction, followed 

 by rather more than 2 feet of darker tawny sand, also highly fossi- 

 liferous. The series closes with a little less than a foot of very dark 

 olive-green sandy clay, with Cerithium, Marginella, Natica, Lucina, 

 Cyrena, &c. 



These beds have been described as " Upper Bagshot " and 

 *' Headon Hill Sands," and the measurements taken vary from 15 

 to 20 feet. A list of works bearing upon them was given by Tawney X 

 when he dissented from a proposal to place them in the Headon 



* Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 573. 



t The lower of the two Becton-Bimny Beds is Wright's no. 19, grey sand 

 without fossils, 20 feet thick. It is present from west of Bectou Bunny to 

 beyond the Coastguard Station. The upper bed is no. 18, tea-green coloured 

 clay, about 25 feet thick, with Oliva, said to differ from all other qualities of 

 bed. It rises on the shore near Long Mead End. and maintains itself to a 

 quarter of a mile east of Becton Bunny, near Barton Gang. Wright, Ann. & 

 Mag. Nat. Hist. ser. 2, vol. vii. (1851) p. 441, and also Proc. Cotteswold Natu- 

 rahsts' Club, vol. i. pp. 129-133 (1853). It is section b of Prestwich, Quart. 

 Journ. Geol. Soc. vol. xiii. (1857) p. 108. 



\ Proc. Cambr. Phil. Soc. vol. iv. part iii. p. 140. 



2r2 



