414 
DR. G. J. HINDE ON BEDS OF SPONGE-REMAINS IN THE 
normal flints of the upper chalk. There are also pockets of a reddish-yellow loamy 
clay which appear to be produced by an alteration of the normal rock. Some portions 
of the beds do not appear to contain calcareous material, in others calcite is present 
and the rock is then harder and denser. When a fractured surface is examined with a 
strong hand-lens it is seen to consist of minute silvery mica-scales, points and rods of 
glauconite, and white powdery siliceous granules. Fragments of sponge-spicules are 
also visible, but these are less numerous than the minute hollow cavities of spicules 
with which the rock is throughout interpenetrated, and to which it owes its porositv. 
These spicular casts are very minute, and it requires careful observation to detect 
them (Plate 40, fig. 7). 
Thin sections of the harder portions of this rock, examined under the microscope, 
still further confirm its organic origin and its derivation from the spicules of siliceous 
sponges. The sections show spicules, mostly fragmentary, irregularly distributed in 
the siliceous and siliceo-calcareous matrix. The points and rods of glauconite can be 
recognised as portions of siliceous spicules replaced by this mineral. The spicules 
which yet remain siliceous are white by reflected, and transparent by transmitted 
light; they are negative to polarised light, and thus show that the silica still retains 
the amorphous colloid condition in which it is present in recent siliceous sponges. The 
silica of the matrix, and also that infilling the empty casts of the spicules, is partly in 
the form of minute discs or globules (the character of which is more fully referred to 
in the sequel), likewise of amorphous silica, and partly of transparent chalcedonic 
silica (Plate 40, fig. 5). 
In the general mass of the rock, the spicules which yet remain intact are firmly 
imbedded in the siliceous matrix, but in the decomposed clayey portions some may be 
obtained by washing, free from matrix. They are principally acerate and trifid spicules 
belonging to tetractinellid sponges, mingled with others of lithistid and hexactinellid 
types. There is a general resemblance to the spicules of the sponge-beds from the 
lower greensand, and to those from the upper greensand of the Isle of Wight and the 
South-Western counties, but at the same time they are notably of smaller dimensions. 
Not only in this locality but generally m the beds of malm or firestone to the north 
and west of the Weald the same minute forms occur. 
The spicular constituents of this rock are not shown with equal clearness in eveiy 
portion of the beds exposed, but, as the nature of the rock is similar throughout, there 
is reason to suppose that it is all of similar origin, and may be regarded as a sponge- 
bed. I could not determine whether the quarry-section referred to, 15 feet 8 inches 
in thickness (4'7 m.), embraces the total* thickness of the malm at this place. 
Notwithstanding the abundance of the detached spicules I did not meet with a 
single entire sponge or even a fragment of one in this bed ; they all appear to have 
* Mr. Topley, in the “ Geology of the Weald,” p. 154, states that the total thickness of the upper 
greensand at this place is 22 feet, but this includes the bed of chloritic marl; Dr. Fitton, in the “ Strata 
below the Chalk,” p. 140, places the total thickness at 25 feet, but he did not himself see the section. 
