\ ee VEO ae 
its original condition the cretaceous ooze was, like that of 
the Atlantic deep sea mud, filled with the spicular skeletons 
of sponges. At the same time they furnish no evidence of 
the hypothesis of Dr. Wallich that alternating periods are 
established during which one of the two predominant animal 
types (Foramenifera and Sponges) gradually overwhelms and 
crushes out the other over indefinite local areas, the strata of 
the chalk in the one case and the intercalated flint beds in 
the other, being the issue of these contests. (op. cit. p. 72) 
The contents both of the Irish and Horstead flints show that 
the sponge spicules are equally as much intermingled with 
foramenifera and other calcareous organisms as in the Atlan- 
tic ooze, and that therefore both these »animal types« flourished 
contemporaneously without alternately choking the life out 
of each other. 
These hollow flints throw no fresh light upon the causes 
which have brought about the arrangement of the nodules in 
definite layers but the perfect state of preservation of their 
contents show that in certain cases at least they were formed 
before there was any great accumulation of overlying material, 
which would have crushed the tender shells inclosed within. 
But whatever may have been the forces which dissolved and 
re-deposited the silica in its present form, it seems evident 
that the delicate skeletons and spicules of sponges have been 
the original source of the material itself. 
