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 Hints 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. 

 1 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 

 is 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 concretionary formation. On the other 

 hand, if we suppose the nodules to have been formed at the hnse of a 

 cluster of growing sponges, which die in all stages of development, 

 then the spicules of sponges in 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 bodv as 



