274 
ProceediDgs of the Royal Society of Edinburgh. [Sess. 
from the fine matter could not even now be attained, white granular 
material clinging persistently to the micro-organisms or remaining in 
small but inseparable particles. After treatment with potash, the lighter 
part of the residue was found to be lath-shaped particles and amorphous 
matter, together with minute fragments of chalcedonified organisms. 
Though it is impossible to estimate the amount, there is no doubt that 
much of the final residue must be considered as of terrigenous origin. 
B 13. — This was a large boulder of firm, grey-coloured chalk, and many 
experiments were made with it. Microscopical examination proved it to 
be a very shelly chalk similar to the last described, but it contained 
a greater number of spheres. Though the rock was permeated with 
soluble silica, the whole of the lime was removed in the acid solution ; 
small masses, however, remained cemented together which required break- 
ing. These, as before, were snow-white by direct light and appeared to be 
of minutely granular or mealy texture. The final residue after treatment 
with caustic potash was almost entirely terrigenous material with a few 
fragments of spicules. By taking a little of the residue every few 
minutes as it was being treated with the potash, it was possible to watch 
the gradual liberation of the lath-shaped particles from the investing 
soluble silica as well as the finer inorganic matter. The cementing 
material (?) appeared to be clear amorphous colloid silica, in this, as in the 
last specimen, not in a crystalline condition. The white appearance is 
probably due to the minutely porous condition of the granular material. 
The heavy residue contained small grains of pale green glauconite ; 
their proportion was, however, insignificant to the mass of the rock. 
B 8. — In a section of this specimen small Globigerinse and Textularians 
are a prominent feature, and there are a few shell fragments, but sponge 
spicules are abundant, and Radiolaria are scattered through that which 
looks like the usual calcareous matrix. Analysis again shows that the 
rock is permeated with soluble silica, and two-thirds of the heavy residue 
after treatment with acid consisted of white granular material. Sponge 
spicules constituted the greater part of the remainder of the residue with 
casts of Foraminifera, cells, Radiolaria, and mineral grains. 
On treating the acid residue with potash most of the white granular 
matter was dissolved, though a few fragments remained in which the 
silica was in minutely crystalline condition. This residue after treatment 
with the potash consisted, in fact, almost entirely of sponge spicules and 
casts of Radiolaria in chalcedony, of mineral grains, and a small amount 
of amorphous terrigenous material. 
A 2. — Fragment of a boulder. Chalk, white, in part soft, easily broken 
