ORDER Oi' THE PAMUNKEY BEDS. 485 



Explanations of pi'qfile, or perpendicular section 



a, a, Level, or surface of Pamunkey river air-line between extremes of 



section, 26 miles. 



b, b, Surface of land, "second low ground" nearest to river. 



1, 1, The lowest, and 8, 8, the highest bed of the whole eocene formation, 

 of marl and gypseous earth of various kinds. 



0, o, Layer of olive earth laying on the raised and denuded ends of lower 



beds, forming the present upper surface of the eocene formation. 

 e, e, Sandy gravel and rounded pebbles, lying beneath the lowest eocene 

 bed. 



1, 1, Lowest bed rich marl, rising above river and exposed at South 



Wales. 



2, 2, Green or gypseous earth, without calcareous matter. 



3, 3, 3, 3, Green or gypseous earth beds, with very small and variable 



amounts of shells, either in thin bands, or very slight general admix- 

 ture. All poor as manure, and mostly not worth using. More shelly, 

 and richer otherwise, where highest and next to 



4, Lower and richer part of the upper calcareous beds of the eocene, 



(designated as L and x and y), in foregoing general description, 

 stony layer (z) at bottom. 



5, Upper and softer part of the good eocene marl poorer in calcareous 



matter, and containing bi-sulphuret of iron, generally. 



6, Green or gypseous earth, with some calcareous matter or poor marl. 



7, Green earth, destitute of calcareous matter, and worthless as manure. 



8, Green earth, with some calcareous matter, or poor marl. 



9, Miocene marl of Hampstead, lying immediately on the eocene bed. 



10, Ordinary miocene marl, lying higher than the Hampstead bed. 



The various beds of this formation, in regard to extent, succes- 

 sion, and particular qualities (as before intimated), are represented 

 mostly upon conjecture. Even of the actual exposures above the 

 water-line (a, a), I have seen but a small extent j and, of course, 

 as to what is below the depth of actual excavations and the river, 

 all rests on conjecture, or reasoning from analogy. Neither is it 

 designed to be conveyed that the different strata or layers preserve 

 the regular proportions of thickness, as represented in the figure. 

 On the contrary, it is more usual for each different layer to vary 

 much in thickness, in a long stretch of distance, and in some cases 

 to " run out," and come to an end. Still, after making due allow- 

 ance for all such sources of uncertainty and error, this figure, and 

 the judicious deductions which every reader may make for the fea- 

 tures of his own locality, may be of great use in searching for the 

 richest layers of marl, and still more in avoiding such labour when 

 certain to be disappointed. According to this conjectural section, 

 if it were possible and useful to sink a shaft, or boring, deep enough 

 on the most eastern point exhibited, every separate layer or bed 

 would be reached in regular succession. It might be as low as 300 

 feet or more but at some depth it is probable that the rich marl 

 (M.) now only known (and accessible) at the north-western extreme, 

 could be reached under the south-eastern, or more than twenty miles 

 41* 



