192 BRITISH JURASSIC SPONGES. 
surface, which have been referred to the horizon of the Great Oolite, were found 
also to contain some small Calcisponges; these, however, appear to be more 
nearly related to the species from the Inferior Oolite at Shipton Gorge than to 
those from the Great Oolite near Bath, and it may be noticed that Mr. H. A. 
Walford has also found that several species of Polyzoa met with in the Richmond 
material associated with the small sponges, likewise occur in the Inferior Oolite at 
Shipton Gorge. 
From the Kelloways Rock and the Oxford Clay proper, no sponges have been 
obtained, but in the different divisions of the Corallian series in Yorkshire, 
included in the zones of Ammonites perarmatus and Am. plicatilis, they again make 
their appearance, and sometimes in sufficient numbers to affect the character of 
the rock. Throughout the entire series only one species of siliceous sponge has 
been recorded, and this is the peculiar Rhavella perforata, Hinde (Pl. XIII, figs. 7 
—’f), whose skeleton is made up of microscopic globate spicules. Hxamples of 
it occur in the Lower Calcareous Grit of Scarborough, and in the higher horizon 
of the Coral Rag at Settrington, Yorkshire. Though definite specimens of this 
sponge are rare, the detached microscopic globates, either of this or of other allied 
species, occur so abundantly as to form the larger part of considerable beds of 
rock and give rise to layers of chert of some thickness. Mr. W. H. Hudleston 
states that the lower part of the Lower Calcareous Grit at Scarborough consists 
of a poriferous mass of siliceous material not unlike a fine-grained sponge cake 
(‘ Proc. Geol. Ass.,’ vol. iv, 1876, p. 384); the porous character being due to the 
solution of the minute, globate, sponge spicules which have left pinhole-like 
cavities in the rock.’ In other instances the globates are preserved in a siliceous 
or calcareous matrix, and from this latter they can be obtained quite free by 
means of acid. The section at Scarborough Castle shows, according to Mr. 
Hudleston, a bed of chert, 3 feet 4 inches in thickness, and beneath this rough 
grits, 30 feet in thickness, belonging to the Lower Calcareous Grit, which are 
largely composed of these globate spicules. Hand-specimens of the grit from 
Falgrave Moor and other places near Scarborough, sent to me by Mr. Fox- 
Strangways, and from Filey, obtained by Mr. 8. Chadwick, are mainly composed 
of these spicules. In the Coral Rag of North Grimston, Yorkshire, the same 
globates occur in great numbers, and Mr. Hudleston attributes the prevalent 
siliceous character of the Rag in this locality to the silica derived from these 
sponge remains. Similar detached spicules, unconnected with any definite form 
of sponge, have been described by Mr. J. F. Blake in the Coral Rag at 
Sturminster Newton, Dorsetshire, and at Hilmarton, near Colne, Wiltshire. 
The Lower Calcareous Grit at Filey, and at Scarborough and the neighbour- 
1 An excellent description of the peculiar characters of this rock is also given by Mr. C. Fox- 
Strangways, ‘Mem. Geol. Surv., Jurassic Rocks of Britain,’ vol. i, Yorkshire, pp. 304 et seg. 
