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MERRILL: FOSSIL SPONGE SPICULES. 
A. Statement of the Questions Involved. 
A detailed statement of the questions involved in this inquiry may be 
of service in directing the mind to the result from the beginning, thus 
placing before the reader the distinct line of thought to be followed. 
The excellent work done on cherts and flints by Carter, Sollas, and 
Hinde in England, and Zittel and others on the Continent, has conclu- 
sively shown that the source of these stones is organic silica, and that 
the principal source of this silica is the framework of siliceous sponges. 
I have therefore assumed this origin for the silica of the flint nodules 
under consideration. 
This conclusion appears admissible from the great similarity of physical 
characteristics of nodules and surrounding materials in the Cretaceous 
of Europe and America, and also from the fact that the included fossils 
are of the same families and genera. The identity of origin assumed, there 
ig still left for us the profitable task of the identification of the organic 
forms, and the comparison of them with the known forms of Europe. 
The following topics, therefore, will be discussed in the order given: — 
1. The identification of the fossils of the groups of animals repre- 
sented. These fossils cover rather a wide range and are significant as 
well as interesting. 
2. As fossils of sponge spicules are the principal organic remains, 
attention is next drawn to a consideration of the condition of preserva- 
tion and character of replacement of these spicules. The forms of 
spicules are then taken up and classified to the genus, where it is pos- 
sible, by comparison with work done by others in this subject. 
3. Since the microscopic structure of flint nodules has not been 
studied before, it would seem that the question of condition and process 
of formation might receive some attention. If we suppose that the 
nodules are segregations of materials from many sponges, collected 
around a nucleus which occupies a position near the centre, then all 
the spicules from centre to circumference would show considerable 
mechanical wear as the result of coneretionary formation. On the other 
hand, if we suppose the nodules to have been formed at the base of a 
cluster of growing sponges, which die in all stages of development, 
then the spicules of sponges în situ, so far as they have escaped the 
process of solution, will be perfectly preserved ; while the spicules from 
the surrounding sponge areas washed in by motion of the water, will 
show more or less mechanical wear. In this case a foreign body as 
