17 
be no doubt that, in some instances, they had been agglutinated in 
separate blocks, much as we now found them, Many were angular 
and unrolled, and had evidently not travelled far from the spots 
where they were imbedded. They were further agglutinated together 
in nodules of all sizes, and of greater or less hardness. 
The variety of material out of which they were constructed—in some 
instances worn or unworn flints, in others pebbles, forming pudding-stone, 
- in others again fine ferruginous grit—evidently served to show that, under 
favourable conditions, almost any material formed the rough substance 
of the stones when brought in contact with the cementing material. 
Those recently taken from their sandy beds were not unusually coated 
with imperfectly solidified sand, merging into the character of the 
parent blocks, the process of accretion seeming to be the gathering 
together of the siliceous particles around the surface of the stones. 
There were doubtless differences in the chemical constitution of these 
consolidations, 
Mr. Maw, in writing of such concretions found in the drift of 
Suffolk, stated that the hardest nodules were resolvable into sand by 
the action of hydrochloric acid, which seemed to imply that the 
cementing material was calcareous ; and one block was found to con- 
tain only a very little lime in the shape of silicate. The Sarsens of 
Wiltshire had been found to be composed of very pure silex ; their 
“structure consisting of pure siliceous sand, agglutinated by a siliceous 
cement. They contained no carbonate of lime; and the trace of 
peroxide of iron found in them was due, probably, to the infiltration of 
ferruginous particles from the neighbouring soil, as the iron did not 
_ penetrate beyond the exterior of the stones, the interior being generally 
_ quite white. There appeared to be a total absence of saline matter. 
The weight per cubic foot was 154lbs. 
There were good grounds for believing that the drifting of these 
stones was coeval with the formation of those widely extended patches 
of deposits, called “ Brickearths,” which had resulted from the breaking 
up of the older Eocenes. These drifts had received able exposition'at the 
hands of Mr. Whittaker ; andalthough many oscillations of level had taken 
place since their deposition, and considerable modifications of climate, 
there was very little doubt that the Brickearths were laid down at the 
close of the glacial epoch, at the time when the valleys were eroding, 
and the face of the land about to be made to assume its present 
_ contour—a period that immediately preceded the advent of man. » 
c 
