450 OLIGOCENE. 



At Stonehenge the outer ring is formed of huge Greywethers ; the Altar-stone is 

 a grey micaceous sandstone, possibly Old Red Sandstone from the neighbourhood 

 of Frome ; while most of the stones forming the inner circle are Diabase, and 

 others are Felsites, Hornstones and Schists, whose source is not known. ^ Sir A. 

 C Ramsay has stated that these are certainly not drifted boulders, and without 

 asserting that they came from Wales or Shropshire, he observes that they are of 

 the same nature as the Igneous rocks of part of North Pembrokeshire, of Caernar- 

 vonshire, and of the Llandeilo flag district of Montgomeryshire, etc., west of the 

 Stiper Stones.^ 



Avebury or Abury, between Marlborough and Calne ; Kits Coty House,^ near 

 Aylesford ; and \\ ayland Smith's Cave or Forge, near Ashbury, south of 

 Shrivenham, are formed of Greywethers. 



OLIGOCENE. 



UPPER EOCENE OR FLUVIO-MARINE SERIES. 



The term Fluvio-Marine Series has been applied to this division 

 because the strata are partly of freshwater and partly of estuarine 

 and marine origin.* They are exposed on the Hampshire coast, 

 but most completely developed in the northern part of the Isle of 

 Wight, where their relations and palteontological contents were 

 systematically worked out by Edward Forbes.* The Series is 

 divided as follows : — 



Hempstead Beds. 

 Bembridge Beds. 

 Osborne Beds. 

 Headon Beds. 



The Fluvio-marine Beds consist of marls, clays, and sands, with 

 occasional beds of limestone, and there is no evidence of any break 

 in the series. 



No members of the Fluvio-marine series have been met with in the London 

 Basin, but attention has been drawn by Mr. Clement Reid to the occurrence of 

 Amber in the Pliocene Beds on the Norfolk coast. It is associated with Jet, and 

 both are probably present as worn fragments washed out of an older and under- 



1 N. S. Maskelyne, P. Geol. Assoc, vii. 138; Wilts Mag. xvii. 159; W. 

 Cunnin'Tton, Ibid. xxi. 141, with notes by T. Davies ; G. B. Greenough, in 

 Conybeare and Phillips, Geol. Eng. and Wales, p. 14. 



2 Explan. Sheet 34 (Geol. Surv.), p. 43. 



3 P. Geol. Assoc, i. 64 ; see also Mantell, Fossils S. Downs, p. 253. 

 * The term Vectian was suggested by Prof Phillips (see p. 365). 



5 Q. J. ix. 259, and Tertiary Fluvio-marine Formations of the Isle of Wight, 

 1856; H. W. Bristow, Geol. Isle of Wight, 1862; Prestwich, Q. J. ii. 223; T. 

 Wri"-ht, Proc. Cotteswold Club, i. 87 ; Mantell, Geol. Excursions round the I. of 

 Wioht,'edit. 3, 1854 ; E. Heljert, Bull. Soc. Geol. France (2), ix. 191 ; C. Evans, 

 P. Geol. Assoc, ii. 162. Some of the earliest observations on the strata were 

 made by Webster (see Englefield's Isle of Wight) ; and also by G. B. Sowerby 

 and Sedgwick, Ann. Phil. 1821 and 1822. 



