11 



group of secondary rocks — and from the numerous and rich beds of 

 bituminous coal which it includes, may with strict propriety be de- 

 nominated the groat secondary bituminous coal region of Virginia. 

 Besides its numerous and widely stretching strata of the above- 

 mentioned material, this favoured region possesses the additional 

 treasure of a saline formation of immense extent, towards its western 

 boundary — and if the limits of the region are not improperly as- 

 signed, a similar formation, accompanied with gypsum and other 

 valuable minerals in the south-west corner of the state. 



(f.) — Pursuing the order in which the several divisions of the state 

 have now been sketched, the Tertiary marl region will first claim 

 our attention. 



TERTIARY MARL REGION. 



The extensive area embraced in this division of the state, though 

 presenting comparatively little diversity in external aspect, includes 

 strata, which, by their fossil contents, unequivocally refer themselves 

 to two distinct geological periods, though they are all without doubt 

 comprised in the general class of tertiary formations. Adopting the 

 names which have been recently applied in Europe to parts of the 

 tertiary series, to which the strata referred to may be regarded as 

 probably equivalent, though without implying any conviction on our 

 part, that such equivalence is in general to be expected in the two 

 continents, we shall indicate by the term Miocene the strata which 

 occur in the eastern and greater portion of this region, and from 

 which the ordinary shell marl is procured, while we will apply the 

 name Eocene to the deposit of an older date existing beneath and 

 west of the preceding, containing fossils of a different character, and 

 characterised by the prevalence in considerable proportion of the 

 peculiar mineral called green sand. 



The first of these, or the Miocene marl district, comprehends all 

 the area from the seaboard or water boundary of the state on the 

 east, to a line conceived to be drawn through Northbury on the Pa- 

 munkey, and Croggin's point on the James river, in a direction 

 nearly meridional, but through what precise points, further observa- 

 tions are necessary to determine. 



The other or Eocene marl district is comprehended between the 

 imaginary line above described and another line passing from the 

 mouth of Acquia creek, through Wales, at the junction of North and 



