On Proto-carbonate of Iron in Coal Measures. 339 
Art. XXXIII.—On the Origin and accumulation of the Proto- 
carbonate of Iron in Coal Measures; by Prof. Wintiam B. 
Rocers.* 
ne of these is seen in the fact that the lenticular ores and 
Strata impregnated with proto-carbonate of iron are in a great 
degree restricted to such divisions of the carboniferous rocks as 
‘include beds of coal or are otherwise heavily charged with car- 
bonaceous matter. This is well shown on comparing together 
the four subdivisions of the carboniferons rocks of the great 
trans-Alleghany coal region, as classified under the head of the 
eral coal series of the Pennsylvania and Virginia geology. In 
the first of these, designated as the older coal measures, the 
Proto-carbonate is found in large amount, both in the shape of 
layers of lenticular ore and diffused through the substance of the 
shaly strata. In the next division above, distinguished as the 
older barren shales, and whieh, as the name implies, is compara- 
‘lively devoid of carbonaceous matter, much less of the proto- 
carbonate is met with. In the third group, that of the ewer 
: ! measures, the ore again abounds, and in the uppermost 
division, or newer barren shales, it has a second time almost 
1Sappeared. 
comiparatively destitute of vegetable remains, we find little ad- 
mixture of the proto-carbonate. On the other hand, the fine- 
grained, flaggy, argillaceous sandstones, which are often crow 
* From Prec. Bost. Soc. Nat. Hist. 
