Top of High 
and Low 
Cronkley. 
178 Professor SepGwick on the 
Specimens from different parts of the bed vary from a dirty white 
to a dark lead colour, and many of them, especially at some dis- 
tance from the trap, contain the organic remains of the metal- 
liferous limestone in great abundance. Over this limestone, comes 
a bed of whet-slate of a yellowish brown colour. By the action 
of the mountain streams, some parts of this bed appear to be 
decomposing, and gradually returning to their original soft earthy 
state. On the brow of the hill, still farther to the north, may 
be seen many beds of limestone, sandstone, and shale, im their 
common unaltered state*. 
At the top of the great terrace of High and Low Cronkley, 
on the south bank of the Tees, the relation of the trap to the 
incumbent strata is still more perfectly exposed. Here, as well 
as in the preceding locality, the trap is surmounted by a bed of 
limestone, which, in some places, is five or six yards thick: but 
the line of separation. is so irregular, that it occasionally rises 
through the limestone, and brings the trap into immediate con- 
tact with a still higher bed of hard white siliceous sandstone. 
In consequence of this arrangement, we find on the plateau of 
High Cronkley, masses of sandstone and of limestone lying like 
irregular patches on the surface, sometimes partially filling up 
the hollows, and sometimes crowning the protuberances of the 
inferior bed of trap. 
In one place above Low Cronkley, the horizontal section 
exposes a mass of limestone about four yards wide, passing like 
a vein between two nearly perpendicular cheeks of trap. The 
appearance is, I have no doubt, deceptive; as there is no trace 
* Two nearly north and south lead-veins, run through the beds above described. 
They were formerly worked down into the whet-slate and granular limestone; but, if I have 
not been misinformed, they became unproductive on approaching the trap. They are now 
worked with advantage in the upper unaltered beds. The vein-stuff is principally composed 
of sulphate of barytes. 
