Geological Society. 1 1 3 



to the deposit in Suffolk, is a platform of nearly regular elevation, which 

 appears to have been worn into ridges and valleys by currents acting 

 in parallel lines from N.E.toS.W., and the cliffs both in the interior 

 and on the coast, are sections of these ridges. The dip of the London 

 clay corresponds with that of the crag, and therefore Mr. Clarke in- 

 fers, that both were acted upon by the same agents, and while they 

 were beneath the level of the sea. 



According to the author's observation, the deposit nowhere extends 

 more than twelve or thirteen miles from the coast, and at Pakefield, 

 where the diluvial clay comes to the very edge of the sea, it disappears 

 as a surface deposit, but is visible at intervals further north, between 

 that point and Cromer. Mr. Clarke also states, that though undoubt- 

 edly crag is discernible here and there, in situ, as a regular formation 

 north of the Waveny, yet he by no means allows that it is regularly 

 stratified, as an undisturbed deposit, between Leiston and Pakefield. 

 He is fully convinced from observation, that the diluvial clay and crag 

 are distinct deposits ; and he is almost equally convinced, that if the 

 crag has any share in the formation of the cliffs between the Blithe 

 and Lake Lothing,ithas been introduced by disturbances of a simi- 

 lar nature to those which are presented in the cliffs of East Norfolk. 

 That the localities in dispute may have been once occupied by crag, 

 there is no reason todeny, but they now present no traces of an undis- 

 turbed deposit. 



To previous descriptions of the structure of the crag, the author 

 states that he has nothing to add, except that where the shells are 

 not visible, the sands contain a slight mixture of calcareous 

 matter. 



He objects to the separation of the beds with shells from those 

 without, and shows that the shifting of a sand -bank, would correctly 

 account for the occasional occurrence of beds of sand 30 feet thick, 

 resting upon strata inclosing testacea. 



Believing that the true rationale of the crag is to be found in the 

 hypothesis of sandbanks, inhabited by testacea, and situated in a 

 tidal way exposed to violent fluctuations of the sea, as well as subject 

 to drifts of extraneous matter from land waters, the author sees nothing 

 extraordinary in the idea that accumulations of sand and shingle may 

 have formed a part of that deposit in which the crag is regularly 

 stratified j but he cannot consent to such accumulations, though con- 

 temporaneous with the crag, being classed under that name, much less 

 can he consent to diluvial clay being also included in it. 



If then, says Mr. Clarke, we assume that in this tertiary sea, sand- 

 banks were formed, around the shelves and under the lea of which 

 testacea collected, lived and died, as at present, many of the phse- 

 nomena of the crag may be readily solved, and we shall not need to 

 wonder why the bivalve shells are found lying with the flat sides to 

 the strata of sand ; why the young are congregated in one group, and 

 the old in another j why pebbles are found covered with balani ; or why 

 the remains of terrestrial mammalia are associated with those of whale* 

 and fishes. 



Third Series. Vol. 11. No. 65. Supplement, July 1837. Q 



