22 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
ber of spicules peculiar to itself that were rarely or not at all found in 
the other nodules. Тһе Monactinellids, especially Figure 7, were found 
in nearly all the slides, and I think Figure 7 was found in every nodule 
examined. Knowing the destruotive effects that even a slight friction 
of these among one another would have on the delicate barbs, we must 
conclude, it would seem, that these spicules have never been moved, but 
have been developed on the spot where they are found. Some of these 
globo-stellates that are broken may have been carried from surrounding 
sponge beds and broken up on the road, but, as these occupy the outside 
chiefly, it is easily seen that such movement and consequent breakage 
would be a natural result. It therefore seems to me that this study is 
a, confirmation of the view taken by Professor Sollas that the flints result 
from the continuous growth of sponges £n situ, and that the presence of 
the minute spicules so perfectly preserved, and which he did not find, 
furnish the strongest proof. I must dissent, however, from his other 
conclusion, that the nodules are replacements of chalk by siliceous solu- 
tions deposited in the interstices. 
In the Texas flints there are comparatively few of the chalk-forming 
organisms found fossil, and these are so isolated that they seem to have 
no connection at all with one another. It is reasonable to suppose that 
they may have fallen into the framework of the sponge and sunk down 
into the siliceous mass on the death and decay of the sponge body. Іп 
one nodule there were four concentric rings of chalk followed by as many 
of silica on the outside of the nodule, The chalky material was silicified 
but not replaced, and it is but reasonable to suppose that such would 
have occurred within the nodule had the nodule been formed by the 
replacement of the chalk as Professor Sollas proposes for tho nodules of 
the English flint. "Therefore, in consideration of the above points, I have 
thought it allowable to suggest that each nodule represents a separate 
sponge bed, in which many generations of sponges have lived aud died 
in all stages of development. On the death of any certain part, the spic- 
ules fell away, many of them down below into the mass at the bottom. 
Here the process of solution went on continually, and nearly all the spic- 
ules were dissolved and few left in the dissolved mass. Why so many 
of the dermal spicules 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 
