362 Rev. W. B. Clarke on the Geological Structure 



The furthest western or inland point at which the formation is visible, is at 

 Layham, near Hadleigh* ; the country beyond being covered by diluvial clay. 

 It constitutes, however, the substratum of all the districts intersected by the 

 estuaries of IheS.E. of Suffolkf,and the coast section fromOrford Ness to Wal- 

 ton Naze (Plate XXXI., fig. 1 to 5 and 7), being everywhere capped by crag, 

 except at Havergate Island, in the Ore. This section is constantly varying in 

 its features, but presented, when I 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, 

 I could not satisfactorily determine. The supply of water obtained from the 

 formation appears to be governed by local phaenomena. At East Bergholt a 

 well was dug, to the depth of 40 feet, in London clay, without success ; but in 

 excavating a cellar at the distance of a few feet, a copious spring was tapped, 

 and conveyed into the well 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 are confined to fishes' teeth, and the occasional occurrence of 

 shells; but in the clay of the West Rocks, off Harwich, fossil turtles have 

 been found. 



4. Crag. — The term crag is applied in Suffolk only to the shelly beds, and 

 the word gravel to the associated beds of pebbles, as well as to the accumula- 

 tions of superficial drift stones. The portion of the country occupied by the de- 

 posit, is bounded on the west by aline, connecting the water-head of the estua- 

 ries ; and the most southern part at which it is now visible are Blackbrook Hill, 

 near Dedham, and Langham. The patch at Walton Naze has been considerably 

 reduced by the partial destruction of the cliffs (Plate XXXI., fig. 4, 5, and 7.). 

 The sand, however, in which the shells occur at Blackbrook, I have traced to 

 Ardleigh Wood near Colchester, and it is said that Danbury Hill, near Chelms- 

 ford, is capped by crag, but I doubt the accuracy of this observation. The gene- 

 ral area of the surface occupied by the formation within the county of Suffolk^, 

 is a platform of nearly uniform elevation, but it has been worn into ridges and 

 valleys, apparently by currents acting in parallel lines from N.E. to S.W., and 

 the cliffs both in the interior and on the coast are sections of these ridges. The 



* See postscript at end of sections, p. 383. 



t For references to detailed sections, see numerical index, p. 368. 



% For references to detailed sections, see p. 368. 



