BAGSHOT BEDS. 449 



sandstone, which from their occasional resemblance in the land- 

 scape to sheep have been popularly termed " Greywethers." They 

 are also known as Sarsen or Sarsden Stones, and Druid Sand- 

 stone : the name Sarsden may be derived from the village of that 

 name near Andover. 



In size these stones attain dimensions of lo or 15 feet across, 

 and from 2 to 4 feet in thickness ; they are roughly oblong. Their 

 texture varies, but they are usually formed of hard saccharoid 

 sandstone, pale-grey, white, or reddish-brown in colour. Fossil 

 roots of Palms (.'') have been observed in the stone. ^ 



These Greywethers are concretionary masses of sandstone that 

 were hardened by siliceous cement in a sandy formation, and the 

 majority of the blocks have been derived from Eocene strata. 

 They are in fact relics of beds which formerly extended over the 

 Chalk Downs of the south and west of England ; in some cases 

 they rest not far from their parent source, in others they have been 

 transported to some distances by the agents of denudation. The 

 strata which may have yielded these blocks are the Reading Beds, 

 the basement-bed of the London Clay, and the Bagshot Sands : 

 and from the last-named formation most of the Greywethers have 

 undoubtedly been derived.- Flint-pebbles and stones, only slightly 

 rolled, sometimes occur in the Greywethers, but large blocks of 

 conglomerate (Hertfordshire puddingstone) are also found. (See 



P- 43I-) 



The occurrence of Greywethers is most conspicuous on the Chalk downs west of 

 Marlborough, in WiUshire, and in Berkshire, but many occur also in the Vale of 

 White Horse, near Wantage.^ 



In Surrey, many Greywethers are obtained from the surface of the Frimley 

 Ridges and other places, where they lie not far apart one from another, some- 

 times in the Upper Bagshot Sands, and sometimes in the superficial gravels. 

 In the latter instances they occur sometimes in a more or less worn condition.^ 

 They are found by sounding the sands and gravel with iron rods. The sandstone 

 is friable when first excavated, but it hardens by exposure. It is broken up into 

 small cuboidal stones for paving or building, and for road-metal. In some places 

 the greywethers are used for gate-posts, stepping-stones, etc. Much of Windsor 

 Castle is built of greywether sandstone. 



At Hampden, and other places, to the north and north-west of High Wycombe 

 there are beds of Drift brick-earth containing masses of greywether sandstone 

 (known as Hampden Stone), which are worked for road-metal, paving, and 

 building.^ Greywethers have also been found in superficial deposits on the Chalk 

 hills near Maidstone, near Southampton, and other places. 



Near Sidmouth large blocks of a siliceous breccia are met with, and pebbles 

 of the same rock, called the Sidmouth pebbles, are picked up on the beach and 

 polished ; similar blocks occur at Portisham, near Abbotsbury.® (See p. 433.) 



1 W. Carruthers, G. Mag. 1885, p. 361. 



^ Prestwich, Q. J. x. 123 ; Whitaker, Explan. Sheet 13 (Geol. Survey), p. 47, 

 Q. J. xviii. 258 ; Ramsay, Explan. Sheet 34 (Geol. Surv.), p. 41 ; Lieut.-Col. 

 W. T. NicoUs, G. Mag. 1866, p. 296 ; Rev. J. Adams, /did. 1873, p. 198 ; 

 T. Codrington, Mag. Wilts Arch. Soc. 1885. 



^ Godwin-Austen, Q. J. vi. 461. 



* T. R. Jones, P. Geol. Assoc, vi. 436 ; Rev. A. Irving, Idid. viii. 153. 



5 Whitaker, Geol. Middlesex, etc. (Geol. Surv.), 1864, p. 66; Morris, G. Mag. 

 1867, p. 457. 



•^ Buckland, T. G. S. (2), i. lOi, ii. 126; Reliquiae DiluvianK, p. 24S. 



29 



