424 
DR. G. J. HINDE ON BEDS OF SPONGE-REMAINS IN THE 
phous silica in minute granules ; there are also grains of quartz-sand, minute scales of 
mica, and some glauconite. The rock is interpenetrated throughout with the empty 
casts of spicules, which give to it its porosity and lightness. A few of the spicules 
themselves also remain, and these are of amorphous silica, like the matrix. The 
specimen is a typical example of a fossil sponge-bed. Its characters correspond closely 
with the upper greensand malm of Merstham, but the gaize contains no calcite, and 
the silica, though amorphous, is not redeposited in the globular form. How far the 
specimen sent me may represent the general characters of the gaize de l Argonne, 
which is stated to be 100 metres (328 feet) in thickness, I am unable to determine, 
but if it is a fair sample of this deposit, it forms an immense bed of sponge- 
remains, which far exceeds in thickness those present in the greensands of this 
country. 
(2.) Montblainville , Meuse. —The specimens of gaize are soft, minutely porous, 
of a bluish-gray tint, with yellowish-gray bands, which appear to be the remains of 
entire sponges, now decomposed beyond recognition. The rock is largely of 
amorphous silica, entirely negative to polarised light, and it is partly present in the 
globular form. The globules or discs are of the same transparent hyaline character 
as those from Farnham, but the majority of them are smaller ; they are from ’006 to 
*02 mm. in diameter. In addition to the remains of entire sponges, the matrix is filled 
with the minute casts of detached spicules as well as some of the spicules themselves. 
The silica of these is amorphous, and appears to be assuming the globular form, like 
that of the matrix. A further peculiarity of these spicules is that the concentric 
layers of silica composing their walls can be detected under the microscope. The 
specimens are from a true sponge-beck 
(3.) Bracquegnies. — Meule (gaize) zone a Ammonites inflatus. —The specimens 
of this rock are extremely light, porous, and friable. The rock is rough to the feel, of 
a greenish-white tint, with numerous green specks in it; it has generally the aspect 
of pumice. Its structure resembles that of the gaize from Grand Pre. The silica 
is largely amorphous, occasionally in the globular form, but usually in minute irregular 
particles. It is throughout filled with spicules and empty spicular casts. According 
to* M. M. Briart and Cornet, this meule de Bracquegnies contains large quantities of 
soluble silica, as well as silica in the form of chalcedony, and judging from the 
specimen forwarded to me by Dr. Barrois, this silica has been derived from the 
solution of the siliceous sponge-spicules with which the rock was filled. The able 
authors above mentioned have very fully described the larger fossils in the meule, 
which appear to be on the same geological horizon as the Blackdown sponge-beds, 
but they do not seem to have noticed the sponge-remains to which the deposit owes 
its principal mineralogical characters. 
(4.) Rumigny, Ardennes.- —Gaize (albien).—Thisrock is hard, of a greenish-gray 
tint, from the coarse glauconite grains with which it is filled. The silica which 
* ‘L’Academie Royale des Sciences, &c., de Belgique,’ tome xxxiv., 1867—70. 
