218 OUR COMMON BRITISH FOSSILS. 



sea-mats attain their minimum of beauty. About two 

 hundred species are said to have been already described 

 from this important formation, most of them belong- 

 ing to the genus Eschara. I have found that the best 

 objects on which to look for Cretaceous fossil sea- 

 mats are the naked tests of such sea-urchins as 

 Ananchytes and Galerites. Very few of these fossils, 

 excavated from the Norfolk Chalk, and then carefully 

 and tenderly washed, but have a sprinkling of fossil 



Fig. 184. Cells of Diastopora Oolitlca (magnified). 



sea-mats over them. Not a few may be found com- 

 pletely invested with them (all but the base), looking 

 as if the " fairy-loaves," as they are called, had been 

 packed away in delicate Honiton lace, and all had 

 been fossilized together. We find these Cretaceous 

 sea-mats actually silicified, which shows what a great 

 chemical change is often included in fossilization. 



We do not lose sight of fossil sea-mats in our 

 British Eocene deposits, but the place to find Tertiary 



