Oh. XIII.] 



NORWICH CRAG PLEISTOCENE. 



Fig. 125. Fig. 126. 



155 



Fig. 12T. 



Nucula Cobloldim. 



Tellina obliqua. 



Natica helicoides, 

 Johnston. 



arvernensis* (see fig. 135, p. 165), a portion of the upper jawbone with. 

 a tooth having been found by Mr. Wigham at Postwick, near Norwich. 

 As this species has also been found in the Red Crag, both at Sutton and 

 at Felixstow, and had hitherto been regarded as characteristic of forma- 

 tions older than the Pleistocene, it may possibly have been washed out of 

 the Eed into the Norwich Crag. 



Among the bones, however, respecting the authenticity of which there 

 seems no doubt, may be mentioned those of the elephant, horse, pig, deer, 

 and the jaws and teeth of field mice (fig. 146, p. 167). I have seen the 

 tusk of an elephant from Bramerton near Norwich, to which many 

 serpulse were attached, showing that it had lain for some time at the 

 bottom of the sea of the Norwich Crag. 



At Thorpe, near Aldborough, and at Southwold, in Suffolk, this fluvio- 

 marine formation is well exposed in the sea-cliffs, consisting of sand, 

 shingle, loam, and laminated clay. Some of the strata there bear the 

 marks of tranquil deposition, and in one section a thickness of 40 feet 

 is sometimes exposed to view. Some of the lamelli-branchiate shells have 

 both valves united, although mixed with land and freshwater testacea, 

 and with the bones and teeth of elephant, rhinoceros, horse, and deer. 

 Captain Alexander, with whom I examined these strata in 1835, showed 

 me a bed rich in marine shells, in which he had found a large specimen 

 of the Fusus striatus, filled with sand, and in the interior of which was 

 the tooth of a horse. 



Among the freshwater shells I obtained the Cyrena consobrina (fig. 26, 

 p. 28), before mentioned, supposed to agree with a species now living in 

 the Nile. 



I formerly classed the Norwich Crag as older Pliocene, conceiving that 

 more than a third of the fossil testacea were extinct ; but there now 

 seems good reason for believing that several of the rarer shells obtained 

 from these strata do not really belong to a contemporary fauna, but have 

 been washed out of the older beds of the " Pied Crag ;" while other 

 species, once supposed to have died out, have lately been met with living 

 in the British seas. According to Mr. Searles Wood, the total number 

 of marine species does not exceed seventy-six, of which one tenth only 

 are extinct. Of the fourteen associated freshwater shells, all the species 

 appear to be living. Strata containing the same shells as those near 

 Norwich have been found by Mr. Bean, at Bridlington, in Yorkshire. 



* Owen, Brit. Foss. Mamm. 211. Mastodon longirostris, Kaup, see ibid. 



