On Proto-carbonate of Iron in Coal Measures. 341 
do occur in this group of deposits, they are found imbedded in lay- 
_ ers of greenish and olive sandstones and dark bituminons shales. 
So, in the southern parts of the belt in Virginia and North Caro- 
lina, where these rocks include seams of coal and extensive beds 
of sandstone and shale containing the remains of plants, the 
usual red color is, found to give place to the gray, olive, and dark 
tints of the old coal measures, and layers of proto-carbonate of 
iron show themselves in the vicinity of the coal seams. 
aken in mass, the red and mottled strata of the unproductive 
coal measures, or of the other groups of red rocks above alluded 
to, would no doubt be found to contain, in an equal thickness, as 
rge an amount of iron as the coal-bearing strata which include 
the layers of carbonate; the difference being that, in the former 
case, the metal remains for the most part diffused through the 
tock asa sesquioxyd, while in the latter, having assumed the 
condition of proto-carbonate, it has to some extent been concen- 
trated in particular layers or strata. According to a rough esti- 
mate of the amount of carbonate ore included in the lower coal 
measures of the Laurel Hill region of Virginia and Pennsylvania, 
derived from a detailed examination of the ores and associate 
