Ch. XXL] OF THE UNITED STATES. 331 



and between the seams of coal. In order to explain this fact we must 

 suppose such shales and sandstones to have been gradually accumulated 

 during the slow and repeated subsidence of the whole region. 

 • It is worthy of remark that the Equisetum columnare of these Virginian 

 rocks appeare to be undistiuguishable from the species found in the oolitic 

 sandstones near Whitby in Yorkshire, where it also is met with in an up- 

 right position. One of the Virginian fossil ferns, Pecopteris Whitbyensis, 

 is also a species common to the Yorkshire oolites.* These Virginian coal- 

 measures are composed of grits, sandstones, and shales, exactly resembling 

 those of older or primary date in America and Europe, and they rival or 

 even surpass the latter in the richness and thickness of the coal-seams. 

 One of these, the main seam, is in some places from 30 to 40 feet thick, 

 oomposed of pure bituminous coal. On descending a shaft 800 feet deep, 

 in the Blackheath mines in Chesterfield county, I found myself in a cham- 

 ber more than 40 feet high, caused by the removal of this coal. Timber 

 props of great strength supported the roof, but they were seen to bend 

 'under the incumbent weight. The coal is like the finest kinds shipped at 

 Newcastle, and when analyzed yields the same proportions of carbon and 

 hydrogen, a fact worthy of notice when we consider that this fuel has been 

 derived from an assemblage of plants very distinct specifically, and in part 

 generically, from those which have contributed to the formation of the 

 ancient or paleozoic coal. 



The fossil fish of these Richmond strata belong to the liassic genus Telra- 

 gonolepis (JEchmodus), see fig. 411, and to a new genus which I have 

 called Dictyopyge. Shells are very rare, as usually in all coal-bearing de- 

 posits, but a species of Posidonomya is in such profusion in some shaly 

 beds as to divide them like the plates of mica in micaceous shales 

 (see fig. 422). 



Fig. 422. 



a. Posidonomya, or Estheria ft b. Young of same. 



Oolitic coal-shale, Eichmond, Virginia. 



In India, especially in Cutch, a formation occurs clearly referable to the 

 oolitic and liassic type, as shown by the shells, corals, and plants ; and 

 there also coal has been procured from one member of the group. 



* See description of the eoal-field by the author, and of the plants by C. J. F. 

 Bunbury, Esq., Quart. Geol. Journ. vol. iii. p. 281. 



f Possibly, as suggested by Prof. Morris (Geol. Journ. vol. iii. p. 275), these 

 delicate bivalves may prove to belong to the crustacean genus Estheria. 



