150 History of the Sarsens. 
rock is covered with Drift. Around the village of Wickham there 
are a great number of Sarsen Stones, all of which have been moved 
from their original position. Some of the blocks contain flint 
pebbles. I ascertained that they were all got from the neighbouring 
fields, and were in no case brought up from a lower level; so that 
they must have originally rested on some of the highest parts of 
the Reading Beds, if not on the top of them, the Wickham outlier 
being very thick. This does not accord with Mr. Prestwich’s 
suggestion that they belonged to the white sand at the lower part 
of this outlier (Q. J. G. S., vol. x., p. 126). I think, moreover, 
that, had these stones been formed from the white sand, some of 
them would be still left in place, and, being so hard, would make 
some feature and be seen on the sides of the ridge. A large flat 
stone near Wormstall Farm must be nearly two tons in weight.” 
Mr. Whitaker notes :—‘“ Mr. Prestwich has come to the conclusion 
that the Greywethers once formed a part of the Reading Beds, for 
the following reasons:—1l. That their distribution is in accordance 
with the range of the Lower-Eocene Tertiaries [see the table at 
page 131] rather than with that of the Bagshot Sands, to which 
they have been referred ; and having thus limited their age to the 
Lower-Eocene Period, 2, that there is no good evidence of their 
belonging either to the Basement-bed of the London Clay or to the 
Thanet Sand, and therefore that they must belong to the intermediate 
Reading Beds. This conclusion is supported by the facts—that the 
occurrence of the Greywethers is proportioned to the development 
of the sand-beds in that formation ; ‘ that the lithological structure 
of each variety is respectively in accordance with the mineral com- 
ponents forming the strata [of the Reading Beds] in the immediate 
vicinity of the place where these rock-blocks are found’; and that 
sandstone has been noticed in place in the Reading Beds. Admitting 
the force of these arguments, I cannot but think, however, that it 
is very probable that some, perhaps very many, of the Greywethers 
have once formed a part of the Bagshot Sands (which formation is 
known to contain beds of sandstone in places), more especially at 
the western end of the London Basin, where the Lower Tertiaries 
are thinner than elsewhere, and where, consequently, the Bagshot 
