Cambridge Philosophical Society. 



of blue drift-clay, cut into abrupt undulations by a network of val- 

 leys. This clay is totally without any symptom of stratification, and 

 is full of fragments of all rocks of the secondary period, including 

 specimens of granite and other igneous rocks. 



Wells sunk in different parts of the county show this drift-clayto 

 have a thickness varying from 200 feet to a few inches ; it seems to 

 thin off from the northern and western parts of the county towards 

 the coast, and only exists in the shape of outliers beyond a line 

 passing through Sudbury, Hadleigh, Bramford, Woodbridge, and 

 Saxmundham ; a line, it may be remarked, nearly coinciding with 

 the edge both of the London clay and of the crag, and approximately 

 passing through the heads of the tidal estuaries of the OrweU, Deben, 

 Ore and Aide. The clay is almost universally underlaid by an un- 

 fossiliferous sand ; and there is reason to conjecture that this sand, 

 of a prevailing red colour, passes out beyond the just-mentioned line, 

 and covers in many places the surface of the strip of land between 

 it and the sea. 



A detailed examination of the Gipping valley reveals a well- 

 marked and connected line of sand cliffs fringing it, and its Codden- 

 ham tributary in particular, at a high level on both sides ; the sand 

 is generally pure white, though often red, horizontally stratified and 

 capped with an unrolled gravel, which evidently owed its existence 

 to the quiet washing away of the drift- clay from its insoluble con- 

 tents. Above Needham Market the valley is channelled in drift- 

 clay, but between Needham and Bramford it is cut through chalk ; 

 and it should be remarked, that the line of sand-hills does not extend 

 up the valley with any great distinctness beyond the chalk. The 

 phsenomena seen at Greeting are not consistent with this sand lying 

 beneath the drift-clay; and the inference is, that it constitutes the . 

 remains of an estuary deposit formed in the valley subsequent to ita .^ 

 excavation in the drift clay. - 



All the other streams west of the Gipping have chalk for their 

 floor during the middle part of their course, thus manifesting the 

 existence of a ridge of chalk running beneath the drift accumu- 

 lations nearly due west and east from Sudbury to Bramford. Di- 

 sturbances evidenced in this ridge, and perhape due to its elevation, 

 are partaken of by the London clay and crag deposits which overlie i 

 it on the east and south. 



In Norfolk the drift- clay attains a greater thickness than in Suf- 

 folk, and towards the north of the county is overlaid by a sand and 

 gravel formation which may be appropriately termed upper drift. 

 The gradual disappearance of this towards the south, together with 

 the thinning away and final extinction of the drift-clay in the same 

 direction, point to a region of greater denuding activity ; it may be 

 an interesting question whether such denudation be in any degree 

 connected with the upheaval of the before-mentioned chalk ridge, 

 or again, whether the sands of the Gipping valley bear any relation 

 to the upper drift of Norfolk. 



March 13. — A paper was read by Prof. Challis on the Eccentricity 

 of the Moon's Orbit ; supplement to a former communication on the 



