DESCRIPTION OF FIGURES ON PLATE 11. 

 FOSSIL SPONGES, &c. 



(BRIGHTON MUSEV.M), 

 One-Foirth Natlral Size. 



1 A Ventriculite witli roots in clialk. At A a deposition of 



Silica is shown, the commencement of a Flint. 



2 Impression of a Ventriculite iu calcined Flint, found in a 



piece of lime. 



3 Fungiform Flint, a Ventriculite. 



4 Siliceous cast of the internal cavity of a Ventriculite in a 



hollow Flint. 



5 Ventriculite. 



G Branching Sponge in Flint. Up : Chalk, Chatham. 



7 Remarkable example of a Choanite (Siphonia) in a matrix 



of Silicified Ferruginous Chalk. The broken and 

 interlaced slender rods are the casts in Flint of the 

 canals which opened into the central cavity. 



8 A beautiful example of a Choanite in grey translucent 



chalcedony. 



9 Test of an echinoderm filled with Flint, the best itself is 



often unaltered carbonate of lime. 



10 A curious Flint passing through the broken test of an 



echinoderm. 



1 1 Interesting example of a Flint in which there is a layer of 



Silica evidently deposited subsequently to the formation 

 of the original mass. 



12 Large Flint broken to show cavity in the interior partly 



filled with a mass of small quartz crystals. 



13 Example of a Flint, not uncommon, in which two or more 



Sponges have formed the nucleus of the deposited Silica. 



