REVIEWS I15 
tion, were found, precluding, Merrill believes, that they could have 
been subjected to any friction or great mechanical movement. From 
the state of preservation of the spicules the conclusion is reached that 
the nodules were formed in situ, and that each nodule represents “a 
separate sponge bed.”” The following is Mr. Merrill’s theory: “On 
the death of any certain part, the spicules fell away, many of them fall 
down below into the mass at the bottom. Here the process of solu- 
tion went on continually, and nearly all the spicules were dissolved 
and few left in the dissolved mass. Why so many of the dermal spic- 
ules are left and the zone spicules nearly all dissolved is hard to account 
for, and I have no explanation to suggest. Many of the spicules 
would doubtless fall outside of the growing mass, and these might be 
dissolved according to the method suggested by Dr. Wallich elsewhere 
quoted, and by movement through the water settle around the masses 
already dissolved, and thus form the concentric rings above referred 
to, and also account for the broken condition of the peripheral spic- 
ules. This would also account for the fact that each nodule had a 
prevailing number of spicules peculiar to itself while a few were com- 
mon to all.” The form and size of the nodules is thus explained : 
“Tf the sponge takes root in the ooze of the ocean and becomes firmly 
imbedded, there will be at its bottom a considerable cavity where the 
bottom part dies. We have no means of knowing how rapidly the 
oozes accumulate, but if they accumulate as rapidly as the dissolved 
silica accumulates, then it would seem that the ooze might enclose a 
pocket of the silica, having grown up around the base of the sponge. 
In this way the flint nodule would grow as the sponge mass may have 
been expected to grow; namely, it would begin small, reach a maxi- 
mum size, then decrease in size, and finally end in a point as it 
began.” 
The theory of the formation of the zones seems weak, because it does 
not appear probable that the spicules would fall with sufficient regularity 
to makeaconcentric ring. According to the theory propounded by Mr. 
Merrill he seems to be of the opinion that the flints stand with their 
long axes vertical. The long axes lie in a horizonal plane. 
The observations of Murray, that sponge spicules collect around 
shells, is noted, and is considered a probable hypothesis, but Merrill 
does not consider it applicable to the nodules studied by him. Mr. 
Hill has noted the occurrence of Monopleura texana as a central 
nucleus of some of the flints found in Comanche county, specimens of 
