S OUR COMMON BRITISH FOSSILS. 



decomposed, such durable limy substances are popu- 

 larly denominated "coral." Similarly with sponges. 



Fiar. 2. 



Fig. 3- 



Figs. 2-4. — Fossil sponge Spicules, from Blackdown and Haldon, all drawn on the 

 scale of ^iith to ri^nn th of an inch. (After H. J. Carter.) 



When alive the outer layer of " sponge-flesh " is 

 usually permeated with myriads of exceedingly small 



