51 



the action of the marl, to ascribe a large part of its efficacy to the 

 supposed sulphate of Jime or gypsum contained in it. To distinguish 

 a marl of this kind from the dark blue Miocene marl, a slight atten- 

 tion to the embedded fossils will be sufficient. The saddle-shaped 

 oyster, characteristic of the Eocene, and never found in the later 

 deposite, would at once determine the bed in which it is found to be 

 of the former description — while the common scallop or clam, which 

 is never seen in the Eocene, would indicate the Miocene character 

 of the bed in which it lies. 



In concluding what I have to say upon this important topic, I may 

 be permitted to throw out the suggestion, that should the deposite 

 of which I have been treating, be found as extensive in its range 

 and as useful as a manure as here anticipated, the districts of the state 

 contiguous to its western limits, as well as the region in which it oc- 

 curs, might be expected to reap important benefits from its employ- 

 ment. Parts of Henrico and Hanover, and the lower part of Louisa, 

 in which no marl exists, would be sufficiently contiguous to the Pa- 

 munkey deposite to avail themselves profitably of its use, and when 

 the projected improvements in this region of the state shall present 

 cheaper and readier means of transportation to the remote parts of 

 the two latter counties, as well as to a portion of Goochland, it is 

 not extravagant to hope that this material may be conveyed to those 

 districts at such a cost as will render it a profitable as it would be 

 an efficacious restorative to the exhausted and sterile soils to which 

 ameliorating applications have of necessity hitherto been denied. 



To other parts of the state in a corresponding position, perhaps 

 similar benefits might be dispensed, and thus most of that portion 

 of the state beyond the reach of the limestone which ranges a little 

 east of the S. W. mountain, would in time be brought under the 

 beneficent influence of the marls of the western limits of the Eocene 

 formation. 



REGION BETWEEN THE HEAD OP TIDE AND THE WESTERN FLANK OF THE 



BLUE RIDGE. 



The various geological features of this extensive division of the 

 state are peculiarly interesting, and'nt the same time difficult of in- 

 vestigation. To trace the limits of the formation of an undoubted 

 primary character, occupying the region towards its eastern border, 

 and to ascertain the extent of the overlying rocks, connected with 



