LOWER AND UPPER GREENSAND OE THE SOUTH OF ENGLAND. 
409 
Sevenoaks. The sponges here, however, do not occur in definite beds as a rule, but 
are distributed irregularly through the deposit, in nodular masses of one or more 
entire sponges enveloped in the sand, which is lightly cemented round them. These 
sponges are lithistids; but while retaining their complete outer form, their spicular 
structures have been dissolved, and only casts in a siliceous matrix remain. 
A single definite sponge-bed does, however, occur in the deposit, but it is not more 
than one or two inches in thickness (‘025 to - 05 m.). It is made up principally 
of relatively large acerate and trifid spicules of tetractinellid sponges irregularly 
mingled together, and with these there are minute skeletal fragments of lithistid, and 
even of hexactinellid sponges. The spicules are but lightly cemented together with 
the quartz-sand by a siliceous cement, so that detached forms can be procured by 
breaking up the softer portions of the bed. The sponges in this deposit were first 
discovered by Professor Prestwick, F.Pl.S., who very kindly directed my attention to 
them and conducted me to the beds. 
Maidstone, Kent .—There are no very clearly marked sponge-beds in the numerous 
exposures of the lower greensand near Maidstone. As a general rule sponge-remains 
are altogether absent in the rag or limestone beds, but in one or two layers of this 
material near the base of the section in Bensted’s quarry, spicules were abundant, but 
they are now replaced by crystalline calcite or remain as empty moulds. The principal 
part of the sandstone or so -called hassock-beds, which intervene between the lime¬ 
stone or rag beds, consists of quartz and glauconite grains lightly cemented together 
by calcareous material, but there are also present other beds somewhat similar in 
appearance, but with a cementing material of chalcedonic silica, and inclosing lenticular 
deposits of chert. In these, sponge-remains are abundant, but usually as empty 
casts. The chert is largely filled with fragments of other organisms as well as sponge- 
spicules, and the sponges are not so exclusively present as to justify regarding the 
deposits as sponge-beds. In some of the hassock-beds, however, there are porous 
siliceous accretions nearly entirely composed of sponge remains, but they are not 
continuous in a single bed. 
On the surface of the fields to the north-west of Maidstone there yet remain 
numerous slabs or fragments of a hard porous siliceous rock, from one to three inches 
in thickness (’025 to ’075 m.), in which spicules can be seen. These fragments are 
very similar to those already described from Godaiming, and like them are evidently 
portions of sponge-beds. 
Sponge-spicules appear to have been more abundant in some of the older quarries at 
Maidstone than they are in those which are now worked, since Sir Richard Owen* 
mentions that they were sufficiently numerous to be detrimental to the hands of the 
workmen, and Mr. BenstedI also states that there were large quantities of them 
in the lower beds of the series. 
* ‘Palaeontology,’ 1861, vol. i., p. 6. 
f ‘ Proceedings of the Geologists’ Association,’ vol. i., 1859-60, p. 58. 
