RH^TIC BEDS AT BEDLAND. 
107 
indicates deeper sea conditions than prevailed farther north 
at Cold Harbour. 
Since Mr. Wickes' paper was read, I have been able, by a 
little digging, to expose the junction of the Black Shales with 
the Tea-green Marls. 
Below the Black Shales the section is as follows : — 
ft. in. 
(iv.) Bed ferruginous band . . . .01 
(iii.) Brown clay 0 8 
(ii.) Sandstone interbedded with green marl . 0 4 
(i.) Tea-green marls (a continuous section, 
not exposed) ..... about 9 ft. 
The most interesting point in this section is the change 
which occurs in the Black Shales towards their base, the 
typical black laminae occurring curiously interbedded with 
pale-green marl the latter predominating as their base is 
reached. It would be difficult to explain this by any 
conditions of sedimentation, and may, I think, be better 
accounted for by oxidation of the carbonaceous matter 
through the agency of iron pyrites. In bed F (i.), in the 
section first described, pyrites occur abundantly, partially 
oxidized to limonite, forming brown partings precisely similar 
to these pale-green ones, and indicating clearly the same 
process at work, only not carried so far. A further con- 
firmation of the supposition is given a few yards from the 
spot where these shales are found, where only the first foot 
of Black Shales can be properly called black, the remainder 
being greenish-brown with black streaks. The two divisions 
are well marked, and I noticed a similar sharp division be- 
tween the pyritoiis shales F (i.) and the overlying shaly 
clay F (ii.) in the first-described section. 
I would suggest that the chemical changes involved are — 
(1) The oxidation of pyrites by air and percolating water. 
(2) The oxidation of the carbonaceous matter by the 
