176 



LYELL'S ELEMENTS OF GEOLOGY. 



Older Pliocene Strata English Crag. 



Fig. 133. 



Faseicularia auruntium, Milne Edwards. Family, Tubuliportdai, of same author- 

 A coral of an extinct genus, from the inferior or coralline crag, Suffolk. 



a. exterior. b. vertical section of interior. 



c. portion of exterior magnified. 



d. portion of interior magnified, showing that it is made up of long, thin, 

 straight tubes, united in conical bundles. 



The general analogy of the crag shells to those now living in 

 the neighbouring seas, between the latitudes 50° and 60o north, 

 is so striking that we cannot hesitate to refer the formation to the 

 Pliocene period ; but, as all conchologists are agreed that more 

 than half the species are extinct or unknown, it is to the Older 

 and not the Newer Pliocene period that they belong. Dr. Beck, 

 after examining 260 species of shells, informs me that the average 

 number of species to genera is such as indicates a temperate cli- 

 mate, a result which is also confirmed by the large development of 

 certain northern forms, such as the genus Astarte (see Fig. 134.), 



Fig. 134. 



Astarte, {Crassina, luara.); species common to upper and lower crag. 



of which there are about fourteen species, many of them being 

 rich in individuals ; and there is an absence of genera peculiar 

 to hot climates, such as Conus, Oliva, Mitra, Fasciolaria, and 

 others. The cowries (Cyprcea) (Fig. 132.) also are small, 



