1 1 2 Geological Society. 



tertiary beds frequently rest upon it; but where it rises into an eleva- 

 tion above the river levels, it is covered altogether by diluvium. 



Plastic clay. — There is some difficulty in separating this deposit 

 from the diluvium of Suffolk. At certain points, however, it displays 

 the samebeds of mottled clay and sands with pebbles, which characterize 

 it in other parts of the kingdom ; and it is occasionally exposed be- 

 tween the London clay and chalk. From its local occurrence Mr. 

 Clarke is of opinion, that it has been subjected to denudating agents, 

 ajid that it has partaken, in part at least, of the dislocations which have 

 affected the chalk. 



London clay. — This formation presents, in Suffolk, the usual cha- 

 racters. At Walton on the Naze and Bawdsey, considerable quanti- 

 ties of pyritous vegetable remains are washed up from a bed below th^ 

 level of the sea; and are said to rival in variety and abundance the 

 Sheppy fossils. The furthest western point at which the formation is 

 visible, is Layham near Hadleigh, the country beyond being covered 

 by diluvial clay. It constitutes, however, the substratum of all the 

 estuaries which intersect the S.E. of Suffolk, and the coast section 

 from Orford Ness to Walton Naze, being everywhere capped by crag. 

 This section is constantly varying in its features, but presented when 

 theauthor examined it, in 1827, the appearance of beds once horizontal, 

 having been upheaved in some places and depressed in others ; but 

 to what extent these disturbances may have been produced by elevatory 

 movements, the action of the sea, or the undermining of land springs, 

 he could not satisfactorily determine. The supply of water obtained 

 from the formation appears to be governed by local phaenomena. At 

 Kast Bergholt, a well was dug to the depth of 40 feet in London clay, 

 without success ; but in excavating a cellar a few feet from the well, a 

 copious spring was tapped, and conveyed into it by a channel. In the 

 river Ore is an island of London clay, in which two wells were sunk 

 through 80 feet of clay, 3 inches of rock and 20 feet of sand. The 

 water rose to the surface, had a strong smell of sulphur, but no saline 

 taste, though it overflowed only during high tide in the river. The 

 fossils mentioned by the author, are confined to fishes' teeth, and the 

 occasional occurrence of shells. He mentions that land animals have 

 undoubtedly been found in the London clay, as the tusk of an elephant 

 at Harwich, but he is of opinion that the greater part of such remains, 

 said to have been obtained from the formation, have been washed out 

 either of the crag or the diluvium. 



Crag. — Mr. Clarke says the terra crag is applied in Suffolk only 

 to the shelly beds, and the word gravel to the associated beds of peb- 

 bles, as well as to the accumulation of superficial pebbles. The por- 

 tion of the county occupied by the deposit, is bounded on the west by 

 a line connecting the water-head of the estuaries ; and the most 

 southern point at which it is now visible is Blackbrooke Hill, near Ded- 

 ham, the patch at Walton Naze having been entirely removed by the 

 partial destruction of the cliffs. Sand, however, containing shells occurs 

 at Ardleigh Wood near Colchester, and it has been said that Danberry 

 Hill, near Chelmsford, is capped by crag; but Mr. Clarke doubts the 

 .accuracy of this observation. The general surface of the area assigned 



