332 EXCAVATION Or SMALL PITS. 



as to form a pit with perpendicular sides, and thrown upon the 

 adjoining firm ground (on 3), whence the carts removed it nearly 

 or quite as fast as supplied from the digging. This small excava- 

 tion served to receive the removed overlay from the next adjoining 

 and larger uncovering (2), which, when pitted, in like manner, 

 received the overlay from a still larger space (3). In this manner, 

 successively digging out small pits with perpendicular sides, and 

 then filling each one with the earth removed to uncover adjoining 

 and enlarged spaces, the whole of the first irregular range (A A A) 

 was worked out, between the stream (x) and the line a b, then the 

 lower limit of the firm overlying surface ground, on which the marl 

 had been thrown for the carts, from the previously dug range of 

 pits. So far, the work had been on the thinner out-running of the 

 strata, and the sloping overlay not any where more than 4 feet thick. 

 But thin as it was, and close to the places where thrown, the re- 

 moval was laborious, owing to the oozing spring-water, and the 

 adhesive clay, made much worse by the quantity of water. Of 

 course, for such small and frequent uncoverings the previous cutting 

 oif of the access of springs was out of the question. This difficulty, 

 caused by the water being necessarily worked up with the clay and 

 other earth, increased with the increased width of the uncoverings, 

 and the distances to throw off the earth. Each small uncovering 

 of marl, after all its overlay had been removed, was separately 

 drained, by a small trench being dug in the marl along its land 

 side, and catching and leading the intercepted oozing springs into 

 the previously made and still partly open excavations. As the 

 marl was thrown up across these draining trenches, they were fre- 

 quently choked by the marl, falling back. This was partially 

 guarded against by laying a thick plank over the trench. Walls 

 of marl, 15 to 20 inches thick, were left between each completed 

 pit and the next one begun, to keep out of the newer work the 

 mud and water which filled the older. But after each pit was 

 finished, more or less of the wall previously left was cut down, and 

 so much of the marl saved. Still, there was much loss of marl in 

 what was necessarily left of these walls. Besides, other losses were 

 sometimes caused by floods from heavy rains, or the breaking down 

 of walls, filling unfinished diggings with water or mud too deep to 

 be worth the cleaning out. 



Along the first range of digging (A A A), the stream was higher 

 than the bottom of the pits, from 2 feet at the beginning (1), to 4 

 feet at the upper end (a). Its water was kept out of the diggings 

 by leaving a narrow wall of marl alongside of the stream. This 

 served as a barrier until each pit was finished ; after which the en- 

 trance of water caused no serious inconvenience. As the pitting 

 was extended up the course of the stream, the thickness of the 

 marl stratum increased to 8 feet. The lowest stony layer ; however, 



