1850.] HAMILTON CAMBRIDGESHIRE MARL. 451 



With regard to the valley drift, the author observes, that the lo- 

 calities in the neighbourhood of Frome could readily supply the 

 various constituents of this heterogeneous gravel. On the east and 

 south-east of Frome the flanks of the chalk range consist of green- 

 sand, and somewhat on the west of Frome the millstone grit and car- 

 boniferous limestone are exposed ; whilst between Frome and Bath 

 the forest marble and the great and inferior oolites occur. Aqueous 

 currents setting towards the north from some region south of Frome 

 would act on the several formations mentioned, and eventually trans- 

 port to the Bath valleys a deposit similar to that now reposing in 

 them. From the account of the disposition of the beds before given, 

 it appears that the portion of the deposit nearer the river was formed 

 during powerful aqueous action, which to a great extent interfered 

 with the law of gravitation, while the portion nearer the Hampton 

 hill was precipitated under calmer circumstances, and, at times, du- 

 ring complete quiescence. These are just the conditions which might 

 be expected to result from a northerly current, the force of which 

 would act more violently towards the centre of the valley, whilst the 

 position of Claverton and Hampton Downs would produce a counter- 

 current or backwater which would afford different degrees of calm- 

 ness. The cause of these northerly currents the author ascribes to 

 the elevation of the central anticlinal axis of the south-east of En- 

 gland, viz. that of the Weald. He considers also that the valley drift 

 was contemporaneous with the excavation of the valleys themselves, 

 and, as evidenced by its organic remains, of the pliocene age. 



The author concludes with some observations on the geological age 

 of the river Avon, remarking that the Avon probably dates its origin 

 from the elevation, and consequent change in the local stratification, 

 of the oolitic hills of Gloucestershire, and that the river, when it first 

 took its present direction, merely flowed over an already formed 

 valley -bed. 



4. On the Occurrence of a Freshwater Bed of Marl in the 

 Fens o/ Cambridgeshire. By W. J. Hamilton, Sec. G.S. 



My attention having been repeatedly directed to a peculiar bed of 

 white, chalky-looking marl, partly overlying and partly interstratified 

 with the black peaty soil through which the East Anglian Railway 

 has been cut between Ely and Lynn, or rather between Littleport 

 and Downham, I determined to examine the nature of the bed. V/ith 

 this view, I obtained a quantity of the marl in question for the pur- 

 pose of examination. The bed is seen soon after leaving Littleport, 

 and may be traced continuously for many miles, varying considerably 

 in thickness, from about a foot, as well as I could judge, to three or 

 four inches. In some places it is seen on the surface, in others it 

 approaches it so nearly as to be turned up with the plough, while in 

 others again it is two or three feet below the surface. Whether this 

 difference is owing to the undulations of the ground or of the bed 

 itself, I was unable to ascertain \ I am, however, inclined to attribute 



