THE TERTIARY FORMATIONS OF YIRGINIA. 349 



becomes quite conspicuous at the Paspitansy hills, in King George, and in 

 the neighbouring parts of Stafford county, adjacent to the line of secon- 

 dary sandstone, which forms the western limit of the tertiary formation. 

 The material forming the superficial strata, in the lower portion of 

 the peninsula, is usually a mixture of sand and clay, in a state of minute 

 subdivision, and more or less tinged with the oxide of iron. Some- 

 times this is intermixed with small gravel, of a ferruginous appearance, 

 but it rarely contains pebbles or boulders of any notable dimensions. 

 The diluvial matter assumes a coarser texture, as we proceed westward, 

 presenting, when denuding forces have not removed the superficial 

 beds, alternate strata of sand and pebbles, the latter varying from a 

 half inch to several inches in diameter. In many places these boulders, 

 derived in great part from the neighbouring beds of sandstone, are 

 strewed profusely over the surface, and, together with the superficial 

 layers of white and siliceous sand, render the soils of the higher por- 

 tions of this district comparatively unproductive. While upon the 

 lower levels, contiguous to the large rivers, or their tributaries, the beds 

 of marl, and their associated sands and clays, mingling their fertilizing 

 materials with the soil, have contributed to impart to it a far higher 

 agricultural value. 



Of the Limits of the Meiocene and Eocene Districts of the Peninsula. 



Bounded on the west by the secondary sandstone, before referred 

 to, the eocene formation extends eastward for some distance down the 

 neck, until at length, with a very gentle eastern dip, it disappears be- 

 low the level of the tide. The most eastern points in which it con- 

 tinues visible, are here regarded as forming the boundary of the for- 

 mation towards the east, and the district included between a line traced 

 through these points and its boundary to the west, is, for convenience 

 sake, designated as the Eocene district; although, at some places within 

 its confines, as in the peninsula of the James and York rivers, beds of 

 meiocene occur overlying the eocene. 



In tracing the boundary of the eocene and meiocene marls, as ex- 

 posed in the neck, several localities, marking the eastern termination 

 of the former deposit, were carefully inspected in the anticipation of 

 discovering beds of meiocene shells abpve them, or immediately be- 



