REMOVING OVERLAY. 343 



of the first graduated range, D, in 1845 ; but some of them were 

 introduced more recently. 



The range B (Fig. II.), when completely uncovered and ready for 

 the carts to descend into, and to be loaded on the surface of the 

 marl, was 20 feet wide, including the space for the narrow drain, 

 along its land-side (c, d, e, e^) for the greater part of its length 

 narrower at the angle (i) and then widened to 26 feet at lower end, 

 to give room for a wagon to turn. The whole length was 255 feet; 

 but of this, 96 at the upper end (c, cT) had but half the overlay 

 removed at first ; the earth being left in an inclined plane, sloping 

 downward from the road (gg) on the surface of the land, to 

 the surface of the uncovered marl. The thickness of the overlay 

 here having been 5 feet ; the graded road served to rise that height 

 in 96 feet of the slope. The same grade was not exceeded in ex- 

 cavating the marl ; and it would have served to descend, if required, 

 two feet lower than the usual level of the bottom of the marl, at 

 the lower end of the digging. The digging and removal of the 

 marl was begun at the lower end (t, e, x) and carried on in succes- 

 sive layers } but always keeping the floor of the pit sloping down- 

 ward towards the lowest end (of), and also laterally towards the 

 land-side (e, e). At the lower end was a short, narrow ditch 

 (e, cc,) serving as an outlet into the stream, which had been deep- 

 ened so as to be lower than the lowest designed digging. Thus, 

 whatever water might get into the digging, from rain-floods, or 

 from the side-drain being choked by caving sand, and thereby turn- 

 ing in the spring-water, it would necessarily keep to the lower side, 

 and flow out at the lower end into the stream. The figures II., III., 

 and IV., show severally the horizontal plan, and the longitudinal 

 and cross sections, or profiles of the work. 



The first improved operation adopted was in removing the over- 

 ly? by us i n g> where practicable and convenient, the plough to 

 loosen the earth, and the scraper (such as is used for road-making) 

 to move it into the finished ranges of pitting. The difference be- 

 tween these and the former modes of hand-labour, with hoes, picks, 

 and shovels, was not accurately observed, nor could it be ; as these 

 large operations were extended through several months (and more 

 lately, through a whole year), at such irregular times as labour 

 could be best spared, and especially when previous rain, snow, or 

 freezing had put a stop to usual farming operations. Any farmer 

 can nearly enough estimate the superiority of ploughing over hoe- 

 ing to loosen earth. The hoeing would certainly cost four times, 

 and perhaps ten times as much as ploughing. The scraper is also 

 very far cheaper than shovels, for removing earth to all distances 

 between 30 and 40 feet. For short distances, for which one throw 

 of the shovel is enough, the latter is the cheapest. The excavation 

 by plough and scraper was not only, as anticipated, much easier 



