OLIVE EARTH. 479 



granite range, which makes the falls of this and other rivers. This 

 marl is darker coloured (nearly black in the bed), and apparently 

 richer in green-sand than the former kinds, and also nearly as rich 

 as the best (x) in carbonate of lime. I found of this bed, in dif- 

 ferent specimens selected by myself from the pits of Messrs. Wm. 

 F. Wickham and Williams Carter, proportions varying from 32.50 

 to 44 per cent. This kind also contains some finely divided and 

 diffused sulphuret of iron ; and consequently, gypsum, if not al- 

 ready present (as I infer is always the case), must be formed from 

 the changes of the sulphuret after the application of the marl. 



This bed, though lying the highest, where exposed, in its pre- 

 sent level and elevation, is the lowest in order of all the different 

 beds of this great eocene formation. Below it is a bed of gravelly 

 sand and rounded pebbles, without any appearance of fossil remains, 

 or marine deposition. 



For some 12 miles (if in a straight line, but following the much 

 longer course of the river), and stretching from the final thinning 

 out of the marl (x, or 4), in Marlbourne farm to the first appear- 

 ance (of M, or 1) in South Wales, the whole interval is filled by 

 different layers and kinds of green or gypseous earth. The general 

 appearance is much like that of Coggius Point, before described, 

 but generally containing some little admixture of shells. For a 

 considerable part of this exposure, this gypseous earth is as desti- 

 tute of shelly matter, and as deficient in other fertilizing matters, 

 as I have found, or supposed, to be the upper or exposed parts of 

 the James river gypseous earth. In some layers there is enough 

 of shelly matter to make from 2 to 5 per cent, of the mass. Also 

 there are some bands of a few inches thick only, quite rich in shells. 

 In other places, there is no carbonate of lime ; and although some 

 gypsum and less potash must be present (as in general of all these 

 eocene beds), this poorer earth (miscalled "marl") has been found, 

 when used as manure, of little effect, and less profit.. 



Overlying all the exposed upper marl and green earth of this 

 whole eocene formation (and also extending south-eastward over 

 the nearest miocene) is an unconformable layer of variable but 

 always **small thickness of what is here known as il olive earth,' 7 

 from its greenish brown colour. (It is designated by the broad 

 irregular band o, o, in the figure.) It varies from a few inches to 

 4 feet of thickness is not uniform in texture but usually very 

 adhesive (as found wet in the bed), and difficult to remove. My 

 observations have satisfied me that this earth was formerly marl, 

 or rather a mixture of all the different layers of marl and green 

 earth now below, which after being washed up by the violent cur- 

 rent of the ancient denuding flood, was, during a cessation of the 

 greatest violence of the current, deposited over Ihe whole before 

 denuded and then bare surface. Subsequently, the violence of tho 



