Ch. XXII.] TRIAS OF THE UNITED STATES. 451 



And is there an undercurrent of heavier saline water annually flowing 

 outwards ? If not, in what manner is the excess of salt disposed 

 of? An investigation of this subject by our nautical surveyors may 

 perhaps aid the geologist in framing a true theory of the origin of 

 rock-salt. 



Trias of the United States. 



Coal-field of Richmond, Virginia. — There are large tracts on the 

 globe, as in Russia and the Atlantic border of the United States, where 

 all the members of the oolitic series are unrepresented. In the State 

 of Virginia, at the distance of about 13 miles eastward of Richmond, 

 the capital of that State, there is a regular coal-field occurring in a de- 

 pression of the granite rocks (see section, fig. 489). It extends 26 



Fig. 489. 



•3. r-J 



2 Ph o 



« • I • 3 I 



og II . I I 



Section showing the geological position of the James Eiver, or East Virginian Coal-field. 

 A. Granite, gneiss, &c. B. Coal-measures. 



C. Tertiary strata. D. Drift or ancient alluvium-. 



miles from north to south, and from 4 to 12 from east to west. Pro- 

 fessor W. B. Rogers formerly referred these strata to the lower part 

 of the Jurassic group ; and this opinion I adopted in former editions 

 of this work, after collecting a large number of fossil plants, fish, and 

 shells, and examining the coal-field throughout its whole area. The 

 plants consist chiefly of zamites, calamites, equiseta, and ferns. The 

 equiseta are very commonly met with in a vertical position more or 

 less compressed perpendicularly. It is clear that they grew in the 

 places where they are now buried in strata of hardened sand and mud 

 I found them maintaining their erect attitude, at points many miles 

 distant from others, in beds both above and between the seams of coal. 

 In order to explain this fact we must suppose such shales and sand 

 stones to have been gradually accumulated during the slow and repeat- 

 ed subsidence of the whole region. 



It is worthy of remark that the Equisetum columnare of these Vir- 

 ginian rocks appears to be undistinguishable from the species found in 

 the oolitic sandstones near Whitby in Yorkshire, where it also is met 

 with in an upright position. One of the Virginian fossil ferns, Pecopteris 

 Wliithyensis, is also a species which has been considered as common to 

 the Yorkshire oolites, although Professor Heer doubts its identity.* 



* See description of the coal-field by the Author, and of the plants by C, J., F. 

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



