MERRILL: FOSSIL SPONGE SPICULES. 29 
referred to, and also account for the broken condition of the peripheral 
spicules. "This would also account for the fact that each nodule had a 
prevailing number of spicules peculiar to itself, while a few were common 
to all. The peculiar form and size of the nodules may also receive an 
explanation here. If the sponge takes root in the ooze of the ocean 
bottom and becomes firmly embedded, there will be at its bottom a con- 
siderable cavity where the bottom phrt dies. We have no means of 
knowing how rapidly the oozes accumulate, but if they aecumulate 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 maximum size, then decrease in size, and finally end in a 
point as it began. The shapes of the flints that I studied indicate that 
such a growth may have taken place. The consolidation of the silica 
into flint and the ooze into chalk may have taken place about the same 
time, but the condition of preservation of the spicules indicates that 
there was very little pressure applied to the spicule before the consolida- 
tion into masses so hard that pressure would not change the structure of 
embedded fossils. 
Mr. John Murray! says that in the deep sea at present many of the 
Foraminifera gather around them spicules of sponges as shells. The 
Pilulina, etc., are covered with tests entirely constructed of cemented 
Sponge spicules, and suggest that this may be the beginning of a con- 
cretion of flint or flint nodule. This, as is true also of several other 
suppositions, is a plausible theory, but it seems that the small delicate 
spicules of the Texas flint nodule could hardly have been preserved so 
perfectly where the amount of movement necessitated by such a process 
had taken place. 
Hence, while recognizing that my conclusion as to the process of 
formation of the Texas flint nodules leaves several points unexplained, 
and although I realize full well its incompleteness, yet I think it accounts 
for more of tho facts than any hypothesis I have seen. 
Summary. 
The variety and mixture of the different, kinds of sponges named in 
the preceding pages make it difficult to tell anything about the depth 
of the ancient cretaceous sea. Geodia, which is so fully represented, 
1 Report of IT. M. S. “ Challenger," Volume on Deep-Sea Deposits, p. 268. 
