POSITION OP MARL BEDS. 307 



bed required, but also that the fossil shells should be sufficiently 

 preserved to be recognised as such at a glance. The most nume- 

 rous, most extensive, and also the richest beds, exposed to the eye, 

 in some of the steep and broken banks of the rivers, and which are. 

 now known to the most ignorant labourer as marl, were then not 

 distinguished from other earth, because the shelly matter was so 

 reduced as not to be obvious to view. 



But as soon as the value of these beds was made known, disco- 

 veries or observations of their presence and accessibility were rapidly 

 extended. And in advance of all scientific instruction (from which 

 the general extension of any such formations might have been in- 

 ferred), marl had been found on thousands of farms, where its pre- 

 semce had not been known or thought of, previous to my earliest 

 publication on this subject. Even in Prince George, and after the 

 highest interest had been excited on this subject, for some years 

 the only known exposures of marl were in either the cliffs, or the 

 neighbouring sloping borders of James River, and in the ravines 

 of the hilly lands of some streams emptying therein. Since, besides 

 other places, under all or nearly all the level swampy borders of 

 the Blackwater and its many branches, marl has been found, at no 

 great depth, though concealed from view ; and numerous extensive 

 excavations have been made, and for great improvements. New 

 discoveries of marl are still continually made in localities where it 

 was not before known. There can be little question of the general 

 fact that marl underlies nearly all the lands between the sea coast 

 and the falls of the rivers, and stretching from Maryland to Florida j 

 and increasing in thickness, and generally in richness also, as pro- 

 ceeding southward. In Virginia, the workable thickness of marl 

 is not often more than 12 feet ; and if in some cases as much as 

 25 feet, it is much oftener less than 8 feet. In South Carolina, 

 I ascertained the extensive bed of very rich marl to be more than 

 300 feet in thickness. 



But generally extended as are the marl deposits through lower 

 Virginia, the overlying earth is most generally too thick for the 

 economical working of the marl below. Under most lands, the 

 marl is more than thirty feet below the surface ; and even if reached 

 by digging, would be covered by spring-water, so as greatly to in- 

 crease the difficulty and expense of obtaining it from such depths. 

 Will these obstacles always debar the proprietors from the benefit 

 of this treasure, through more than half the great region under 

 which it lies, now useless and concealed? I think not. Though 

 it would be ridiculous now to propose such undertakings, it will 

 at some future time be found profitable to descend to still greater 

 depths for good marl ; and shafts will be sunk, and the water and 

 the marl will both be drawn up by machinery worked by horse- 

 power or steam engines, and the excavations conducted in the same 



