316 ANNUAL OF SCIENTIFIC DISCOVERT. 



divisions of the coal measures which have been but slightly charged with 

 vegetable matter, as, for example, the barren shales of the Serai Coal Rocks, 

 before alluded to, contain much red material, both in distinct strata and 

 mottling the general mass, and are throughout more or less impregnated with 

 the sesquioxide. 



A like general law, as to color, would seem to apply to the other great 

 groups of sedimentary rocks which include in particular beds accumulations 

 of vegetables, or other organic exuvias. Thus, in the New and Old Red Sand- 

 stone formations, which generally include so large a proportion of sediment 

 colored by the red oxide of iron, organic remains are of comparatively rare 

 occurrence, and when present, are met with almost exclusively in the grey 

 and olive and dark colored strata, which are interpolated in certain parts of 

 the great masses of the red material. This relation is beautifully shown in 

 the middle secondary rocks of the Atlantic slope, which extend in a pro- 

 longed belt from the Connecticut Valley into the State of South Carolina. In 

 strata of red sandstone and shale, which form the chief part of the mass, vege- 

 table or animal exuvias are almost entirely absent. But the remains of the 

 fish and impressions of carbonised parts of plants occurring in this group of 

 deposits are found embedded in layers of greenish and olive sandstones, and 

 dark bituminous shales. So in the southern parts of the belts in Virginia 

 and iv rth Carolina, 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 grey, olive, and dark tints of the Old Coal 

 Measures, and layers of proto-carbonate of iron show themselves in the vici- 

 nity of the coal seams. 



Taken in mass, the red and mottled strata of the unproductive coal mea- 

 sures, or of the other groups of red rocks above alluded to, would no doubt 

 be found to contain, in an equal thickness, as large 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 rocks as a sesquioxide, while in the latter, having assumed the condition 

 of proto-carbonate, it has to some extent been concentrated in particular 

 layers or strata. 



In attempting to explain the origin of proto-carbonate under the conditions 

 above described, it is important to keep in view the fact of the diffusion of 

 this compound through many of the strata as a general constituent, and the 

 frequent preservation, even in layers of the ore, of the lamination of the con- 

 tiguous rock. The supposition of its being a chemical deposit formed from 

 springs charged with carbonic acid, and holding proto-carbonate in solution, 

 is evidently inconsistent with these conditions, and not less so with the fact 

 of the great horizontal extension of individual beds of ore and impregnated 

 shaly rocks. 



In view of these various considerations it may be concluded 



First. That throughout the coal measures and other groups of rocks above 

 mentioned, as well as in the portions containing coal and diffused vegetable 

 and animal matter, as in the barren parts, the original sediment was more or 

 less charged with sesquioxide of iron, and 



