OF NORFOLK AND SUFFOLK. 317 



by which it is almost everywhere covered. It is only in some 

 valleys, like that of the Yare, where denudation has extended 

 down to the fundamental chalk, that the crag is partially ex- 

 posed at the surface. 



The various excavations made for chalk and sand at Bra- 

 merton and Whitlingham, on the right bank of the Yare, and 

 at Thorpe and Postwick, on the left bank, places within four 

 or five miles of Norwich, all agree in presenting beds of sand, 

 loam, and gravel, in which we observe a mixture of marine, 

 land, and freshwater shells, with ichthyolites and bones of 

 Mammalia. It is clear that these beds have been accumu- 

 lated by successive deposition at the bottom of the sea, near 

 the mouth of a river. Mr. Woodward, in his account of the 

 Norfolk crag, has described the drilled surface of the chalk at 

 Postwick, showing that it had remained for some time expos- 

 ed to the action of marine perforating animals, before the crag 

 was thrown down : and similar facts were pointed out to me 

 by the Rev. Thomas Clowes, of Yarmouth, respecting the 

 chalk at Whitlingham. That gentleman presented me with a 

 fragment of chalk, perforated to the depth of several inches by 

 the Pholas crispata, the shell still remaining at the bottom 

 of its cylindrical cavity, the upper part of which was filled 

 with loose sand, which had fallen in from the incumbent crag. 

 The chalk of this place when bored by the Pholas, was either 

 exposed in the bed of the tertiary sea, or at least was not yet 

 covered by a considerable thickness of sand and loam. 



Among other observations which prove the gradual depo- 

 sition of the tertiary strata themselves, I may mention that 

 Capt. Alexander found the tusk of an elephant at Bramerton, 

 to which there were many Serpula attached ; a fact which 

 also demonstrates, together with many others, that the bones 

 of quadrupeds were really washed down into the sea of the 

 Norwich crag, and were not introduced afterwards by diluvial 

 action, as has been sometimes suspected. 



Although many freshwater shells have, by dint of careful 

 search, been detected in the Norwich beds, they are never- 

 theless rare in comparison with the marine Testacea, and the 

 terrestrial species are still more rare. Mr. J. B. Wigham 

 however informs me, that in one of the beds at Thorpe, near 

 Norwich, there is a great predominance of freshwater shells, 

 most of which cannot be preserved, as they fall to powder on 

 being exposed to the air. In the pits of Thorpe last men- 

 tioned, the same gentleman found the tooth of a Mastodon in 

 the bottom of the deposit, near the chalk, together with pec- 

 tens and other marine shells. He also discovered, in 1838, 

 at Postwick, together with the remains of fish, and marine 



