288 REMOVING OVERLYING EARTH. x 



and rising 7 feet above the lower end of the road, it may be con- 

 venient to make a branch to the road running on a level to the top 

 of the marl. This branch will be used until the lowering of the 

 upper marl, by its excavation, shall render the lower branch of the 

 road again more suitable. This range of the marl is drained, 

 worked out to the level of a t, and then the lower part (r, r,~) ex- 

 cavated in successive perpendicular pits, in the same manner as the 

 previous range. Then a third range of overlay (</) is dug and 

 thrown off into the finished previous excavation (/, r, r) ; and by 

 its increased thickness perhaps fills it up as high as the top of the 

 niarl stratum. But this does no serious harm. It will however 

 require the leaving a wall of marl (x, x) when digging out the 

 marl belo^ (7i) to keep out the earth and water of this heap ; and 

 also cross walls for support, between the lower perpendicular pits. 



It will now be much more laborious to uncover another range 

 (at i), still deeper in the hill-side ; and it will become a question 

 for the operator to decide, whether to proceed farther with this 

 work here, or to begin another uncovering in some more favourable 

 situation. 



For any extensive operation, it is much cheaper to take off a 

 cover of earth 20 feet thick, to obtain marl of equal depth, than 

 if both the covering earth and marl were only three feet each. 

 Whether the cover be thick or thin, two parts of the operation 

 are equally troublesome, viz. to take off the mat of roots, and per- 

 haps some large trees on the surface soil, and to clean off the sur- 

 face of the marl, which is sometimes very irregular. The greater part 

 of the thickest cover would be much easier to work. But the most im- 

 portant advantage in taking off earth of ten or more feet in thick- 

 ness, is saving digging by causing the earth to come down by its 

 own weight. If time can be allowed to aid this operation, the 

 dryest earth will mostly fall, by being repeatedly undermined a 

 little. But this is greatly facilitated by the oozing water, which 

 generally fills the earth lying immediately on beds of wet marl. In 

 uncovering a bed of this description, for one of my early operations, 

 where the marl was- to be dug 14 feet, and 10 to 12 feet of earth 

 to remove, my labour was made ten-fold heavier by digging 

 altogether. The surface bore living trees, and was full of roots 

 there was enough stone to keep the edges of the hoes battered 

 and small springs and oozing water came out everywhere, after 

 digging a few feet deep. A considerable part of the earth was a 

 tough, adhesive clay, wet throughout, and which it was equally 

 difficult to get on the shovels, and to get rid of. Some years after, 

 another pit was uncovered on the same bed, and under like circum- 

 stances, except that th^ time was the last of summer, and there 

 was less water oozing through the earth. This digging was begun 

 at the lowest part of the earth, which was a layer of sand, kept 



