396 MESOZOIC FLORAS OF UNITED STATES. 



spar, producing a clearly defined arkose. Clay balls are at times distributed in 

 considerable numbers through the arenaceous beds, which in places contain lenses 

 of gravel, sometimes with cobble stones. Frequently the sands pass over into 

 sandy clays and these in turn into more highly argillaceous materials which are 

 commonly of light color, but at times become lead-colored, brown, or red, and not 

 unlike the variegated clays of the Patapsco formation. Those arenaceous materials 

 which lie adjacent to ferruginous clays are not infrequently indurated by hydrous 

 oxides of iron, forming ferruginous sandstone. The more arenaceous deposits are 

 commonly cross-bedded, and the whole formation gives evidence of rapid deposition. 

 (See pp. 481-482.) 



This description would answer well for the James River and Rappa- 

 hannock series by omitting the reference to the coloring effects of iron. 

 It leaves out, however, the clay lenses and lignite beds yielding fossil 

 plants that occur in the regular sedimentary beds in both the James River 

 and the Fredericksburg regions. They describe the Arundel formation as 

 follows : 



The deposits consist of a series of large and small lenses of iron ore-bearing clays 

 which occupy ancient depressions in the surface of the Patuxent formation. These 

 clays as most typically developed ("blue charcoal clays" of the miners) are drab 

 colored, tough, and frequently highly carbonaceous, lignitized trunks of trees and 

 limbs lying horizontally strongly compressed and frequentlj^ charged with or inclosed 

 by carbonate and sulphide of iron. Sometimes these trunks are encountered in an 

 upright position, with their larger roots still intact. Scattered through the dark 

 clays are vast quantities of nodules of iron carbonate, at times reaching many tons 

 in weight, and known to the miners as "white ore," "hone ore," or "steel ore." 

 In the upper portions of the formation which have been exposed to atmospheric 

 influences the carbonate ores have sometimes to considerable depth changed to 

 hydrous oxides of iron, which the miners recognize under the name of "brown" or 

 "red" ore. Under these conditions also the originally drab-colored clays containing 

 the carbonate ores have suffered a like chemical change, resulting in red or variegated 

 clays. Where these clays chance to contain but little lignite the iron ore may 

 consist almost entirely of these oxides. 



Here again the presence and peculiar influence of large quantities of 

 iron obscure the resemblance of these beds to the clay lenses and lignite 

 beds of the Older Potomac in Virginia, with which they are otherwise 

 identical both in character and in mode of occurrence. But iron is not 

 wholly wanting in the same clay deposits in Virginia. Professor Fon- 

 taine has reported its occurrence on Powells Run and near Cockpit Point, 

 and I have seen a bed near Bush Hill, not far from Alexandria, where the 



