Review of Recent Geological Literature. ">•'► 
The alteration from the axial canal has been quite as active as that 
from the outside, and in some cases is even more important. The re 
suit is that the spicules become at many points merged into the ground 
mass : and in places they are entirely altered, so that only their outlines- 
can be distinguished as faint markings in the amorphous silica. 
Many'of the spicules of the dermal layer, however, are perfect, even 
to the minute barbs. The silica of these spicules is perfectly trans 
parent, and varies in color from a light brown to a dark yellow. Only 
one case was found where the silica had been crystallized into the 
chalcedonic variety ; and it is noteworthy that in this case the form 
was not perfectly preserved. Professor Merrill is in doubt as to whether 
the silica of the perfectly preserved spicules is in the original colloidal 
state or has been crystallized into the amorphous mineral form, hut in- 
clines to the former view. 
In considering the theory advanced for the formation of these nod 
ules it is well to remember that only three specimens, and these all from 
a single locality, were examined : and that, as the writer emphasizes, 
the conclusions are not intended as a general theory. In this ease the 
theory is certainly worthy of attention. It is that "each nodule 
represents a separate sponge bed, in which many generations of sponges 
have lived and died in all stages of development.*' The spicules which 
continually fall around the base of the sponge, as the death of certain 
parts comes on. become consolidated in a mass which ultimately be- 
comes a •• nodule.'" The abundance and perfection of the fragile de-r 
mal spicules show that they have not been carried far from the original 
livingmass; and the fact that each nodule was found to contain an 
abundance of •• spicules peculiar to itself and rarely or not at all found 
in the other nodules," is very strong evidence in favor of the theorj ad 
vanced. As to other circumstances which contributed to the growth 
of the nodules, it is noted that there were found in each specimen ex 
amined a Dumber of spicules of varying species, which show the effects 
of abrasion, and which possibly were derived from some other sponge 
mass: and that a considerable pail of the silica was probably deposi 
ted directly from sea water, in a gelatinous condition. This silica tnighl 
come from the dissolved spicules of the parent sponge, or from silica 
collected at large on the sea bottom and finally deposited around a con 
venient nucleus. 
In regard to the conditions of deposition of the chalk, as shown by 
the study of the Hints, the writer concludes that the (lint horizons 
represent a definite and peculiar set of conditions : that the conditions 
Were not those of the deepest Sc;i. yet beyond the continental shelf. 
.1 . i-:. s. 
Crystallography: .1 Treatise on the Morphology of Crystals. Bj \. 
Stokv Maskki.vm:. (12mo, 52] pp., Oxford. 1895.) This work treats 
simply of the external or morphological characters of crystals, but does 
not proceed to their specific applications to actual minerals, nor t<> ;i 
discussion of t he physical properties of crystals, either mathematical or 
