Coralline Crag. 



271 



an area of about 20 miles in lengtjj, between the Kiver 

 Sfcour and Aldborough. It is generally not more than 

 60 feet in thickness. It consists in places almost 

 entirely of Polyzoa (formerly called Corallines, whence 

 the name, Coralline Crag), and elsewhere, in great part, 

 of broken and entire shells, fragments of Echini, &c. 

 Only four genera of Corals are known, all, according 

 to the lists of Mr. Etheridge, of extinct species, and the 

 same authority gives about 140 species of Polyzoa. The 

 genera of Mollusca are almost entirely recent. The 

 general character of the climate seems to have been 

 milder than at present. 



According to the researches of Mr. Searles Wood, 

 modified by Mr. Gwyn Jeffreys and Prof. Prestwich, the 



FIG. 52. 



Fasciolaria aurantia. G lycimeris angusta. Terebratula grandis. 



Group of Coralline Crag Fossils. 



Coralline Crag contains 316 species of Mollusca, only 5 

 of which are Brachiopoda, Argiope cistellula, Lingula 

 Dumontieri, Orbicula lamellosa, Terebratula grandis, 

 and Terebratulina caput-serpentis. Of the Lamellibran- 



