DRY AND WET MARL BEDS IN HILLY LANDS. 285 



finely divided. Many of these richest and also almost easily worked 

 bodies of niarl are in the middle range across the rivers and the 

 marl region of Virginia; for example, in the counties of Nanse- 

 mond, Isle of Wight, Surry, James City, York, New Kent, and 

 the lower part of King William. Under these very favourable cir- 

 cumstances, special directions for working such marls would be 

 superfluous. The labours required are as simple, and almost as 

 cheap, as the digging and carting away -of earth from a hill-side to 

 construct a mill-dam. 



II. The second class of exposures and diggings is usually of much 

 poorer marl, and attended with much more difficulty and cost than 

 the preceding. In high lands, cut through by deep ravines, or 

 narrow valleys, the natural " out-croppings" of the marl are usually 

 low down the sides, or at the bottoms of steep hill-sides, the marl 

 often wet from springs oozing over the top, and also from water 

 percolating slowly through the mass of marl. The lower adjacent 

 ground^ also wet, by springs or streams. The overlying earth is 

 very thick, and costly to remove ; and a steep or a long-ascending 

 road is required to draw the marl to the higher lands where it is to 

 be applied. 



In hilly lands, the bed of marl usually "crops out" on the 

 swells, or convex curves of the hill-sides, and thus is naturally ex- 

 posed to view. If this is at a considerable elevation above the bot- 

 tom of the ravine or narrow valley which is usually at the foot of 

 the hill, the marl will generally be dry. But its being dry will 

 depend on some one of the following conditions : 1st. When the 

 overlying beds of earth have not enough extent of surface to allow 

 springs to be formed by infiltration of rain-water; or there is no 

 impervious bed, either of the marl or its overlay, on which spring 

 water can be borne, if it flows from distant sources : 2d. Or even 

 if there be any such impervious and water-bearing stratum, that its 

 " dip" is in a direction leading from the " out-cropping" of the 

 marl; so that all spring- water, or infiltrated rain-water, must 

 necessarily flow in a direction leading from the exposure. In the 

 reversed circumstances, the marl will be wet, and proper drainage 

 of the pits will be necessary. Bodies of marl of this second class 

 are most common in the high and broken lands lying between the 

 localities named above, and the falls of the rivers. 



III. The third class of marl generally belongs to the more level 

 lands, but in some cases to the low bottoms and ravines of the 

 highest and most hilly. But in either case, the surface of the marl 

 is lower than that of all the surrounding land (unless perhaps of 

 the mere outlet for the water) ; and the excavations and the roads 

 all need careful and perfect drainage. 



I will now return to the consideration, principally, of excavations 

 of the second class ; though they will in part suit also for the third 

 class. 



