Review of Recent Geological Literature. 53 
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¬ 
sult 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, but 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 case 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 der¬ 
mal spicules show that they have not been carried far from the original 
living mass ; and the fact that each nodulfe 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 theory 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 number 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 part of the silica was probably deposi¬ 
ted directly from sea-water, in a gelatinous condition. This silica might 
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 flints, the writer concludes that the flint horizons 
represent a definite and peculiar set of conditions ; that the conditions 
were not those of the deepest sea, yet beyond the continental shelf. 
J. e. s. 
Crystallography: A Treatise on the Morphology of Crystals. By N. 
Story-Maskelyne. (12mo, 521 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 to a 
discussion of the physical properties of crystals, either mathematical pip 
