LOWER AND UPPER GREENSAND OF THE SOUTH OF ENGLAND. 
421 
scythes. The chert in these beds is of the same character as that which has been 
already described from Ventnor and elsewhere. Spicules are abundant in it, but 
their walls are frequently dissolved, and they are now largely represented by their 
infilled canals (Plate 40, fig. 3). This chert is accompanied, and frequently inclosed, 
by the hard, harsh, porous siliceous rock filled with spicular cavities so generally 
present. In some places this description of rock has been naturally broken up, so as 
to form beds, five or six feet in thickness, of small irregular fragments having a 
pumicedike aspect. 
In addition to the chert and porous siliceous rock, some of the sponge-beds in this 
district consist of a hard, whitish, massive rock, of a granular character, filled with 
spicules of a white porcelanic tint. The rock appears to be nearly entirely siliceous, 
the silica is partly chalcedonic and partly amorphous, and in the globular form. The 
spicules are of amorphous silica, similar to those at Warminster. Small cavities in 
this rock are filled with spicules partially cemented together. 
The sponge-beds of this locality are distinguished by the absence of calcite and the 
small proportion of glauconite and mica present in them. Their organic character 
does not appear to have been hitherto noticed, although they have excited much 
attention, owing to the fact that over an extensive area numerous conical pits have 
been made in them to extract the harder portion of the beds for economical purposes, 
and these pits have been surmised to be the'"' remains of primitive dwellings. 
Blachdown Hills, Devonshire .-—The beds of upper greensand age exposed in the 
higher portion of the Blackdown Hills have formed the subject of numerous memoirs, 
in which some reference is made to the occurrence in them of sponge-remains. The 
detached spicules met with here and at Haldon were first described and figured by 
Mr. E. Parfitt,! and later in a more complete manner by Mr. H. J. Carter, F.ft S.,J 
but these authors do not describe in detail the beds in which they occur. The beds have 
formerly been extensively worked for whetstones and for building, and Dr. Fitton § 
gives full details of the beds employed, and the mode of manufacture of the whet¬ 
stones, without, however, noticing their organic character. 
The basal beds of the greensand consist of a fine-grained yellowish sand-rock, which, 
according to Mr. Downes, [| is 30 feet (9m.) in thickness. This is overlaid by a series 
of beds of sand and siliceous rock varying from 12 to 20 feet (3'6 to 6 m.) in thickness, 
which contain the so-called concretions used for whetstones. These are of a greenish 
tint when moist, and gray when dry. The rock is porous, very harsh to the feel, 
* ‘ Proceedings of the Somerset Archaeological and Natural History Society,’ vol. xv. ; also “ Remarks 
on the Pen Pits and other supposed Early British Dwellings.” By H. B. Woodward, in the ‘Midland 
Naturalist,’ 1883. 
f ‘ Transactions of the Devonshire Association for the Advancement of Science, 1870.’ 
+ Ann - Mag. Nat. Hist., s. 4, vol. vii., 1871, p. 112. 
§ “ Strata below the Chalk,” p. 236. 
|| Quart. Journ. Geol. Soc., vol. xxxviii., p. 80. 
MDCCCLX XXV. :3 i 
