286 



EXCAVATION OF WET MARL. 



There is a general dip of the marl to the east, through lower 

 Virginia. But this so slight, and irregular withal, that it does not 

 always direct the course of the spring-water above according to the 

 general course of the dip. At each particular locality, the marl 

 stratum may be considered as nearly horizontal. The upper sur- 

 face of the dry marls is often very irregular in outline, owing to 

 the washing operation of ancient currents of the sea, or later floods, 

 and whirpools, subsequent to the deposition of the beds of shells. 



Unless very sandy and poor, and also oozy, all our marls are 

 sufficiently firm before being dug, for the sides of a pit to stand 

 secure when cut perpendicularly. The dry beds, of course, are 

 much easier to be worked than the wet. Where the bed is dry, 

 no directions are required for pit- work; except that the pit shall 

 -be long enough to allow the carts to descend therein, and to rise 

 out, loaded, on a graduated and gently sloping road-way. This will 

 obviate the necessity existing when pits are short and steep, of 

 twice throwing the marl first out of the pit, and afterw^ds into 

 the carts. No machine or contrivance yet known will serve as 

 well for cheapness to raise marl from the bottom of a pit, or dig- 

 ging, as a cart ; and no care or labour will be lost in draining and 

 enlarging the pit, and graduating the ascent out from it, if there- 

 by carts can easily and safely draw from the bottom. These re- 

 marks may apply to any excavation made by sinking pits below 

 the level of the general surface. 



Profile j or cross-section of marl diggings, of class II. 



Explanations, 

 b, a, Face of hill-side. 

 s, Stream, or bottom of valley. 

 p, e, /, h, m, Bed of marl, out-cropping at c. 

 m, m, Bottom of workable marl. 

 o, d, ff, Overlying earth. 



I will describe an ordinary case of hill-side excavation. 



