26 OUR COMMON BRITISH FOSSILS. 



Surrey, these sponges are very abundant ; but they 

 have undergone a chemical metamorphosis, and have 

 been converted into phosphate of lime to more than 

 fifty per cent. On this account they are worked, and 

 ground up into artificial manure, or super-phosphates. 

 At Farringdon, in Berkshire, and at Warminster, we 

 have the geologically famous "sponge-gravels," an 

 ancient sea-bed, with whole and broken shells, frag- 

 ments of Echinoderms, etc., through which is dispersed 

 an abundance of fossil sponges. That called Manon is 

 common, and the quarrymen term it " petrified salt- 

 cellar." I have often noticed that when fossils obtain 

 popular names, it is a sign of their abundance. In 

 the Upper Greensand at Folkestone, the fossil sponge 

 termed Scyphia meandrina is especially abundant 



Polypothecia is one of the commonest of the fossil 

 sponges met with in the Greensand at Warminster. 

 It is a branched sponge, allied to those known as 

 Spongites, and it puts one in mind of our common 

 British Chalina, so abundant along our coasts. When 

 found it is usually of a stony texture, but sections 

 of it show it to belong to the lithistids. 



One of the most gigantic of probable sponges is 

 that called Paramoudra, abundant in the chalk near 

 Norwich. There is now little doubt this singular 

 object was a sponge. It is frequently found in the 

 chalk, always extending upwards in a perpendicular 

 fashion to the height of five or six feet, and having 

 a basal diameter of two feet. Its appearance is like 



