ADVANTAGES OP GRADUATED PITS. 347 



served to keep the marl as dry as was possible for a naturally moist 

 and extremely absorbent bed. This preservation from all extra- 

 neous water, as well as losing some of its own by exposure, rendered 

 the, marl easier to dig and to load ; and something lighter of car- 

 riage.' 



Further the digging was no longer impeded by the necessity 

 of having to leave, shape, and secure cross-walls, which had before 

 caused much trouble, and much loss of marl. Now there there was 

 but one wall to be left, which was along the whole length (o, Fig. 

 IV.), to keep out the earth and water which filled the old diggings ; 

 which wall was afterwards cut down, and mostly saved, in the 

 closing operations of each range, in succession. The unlimited 

 room for their work permitted the pit-men to dig the marl in much 

 larger masses, which saved much of the labour of digging, and 

 something in that of loading. For the earthy portion of this marl, 

 compact as it is, is composed of thin horizontal laminae, the result 

 of slow and uniform sedimentary deposition. In consequence, it 

 may be cleaved in the direction of its " grain" much more easily 

 than cut or fractured in any other direction. This facility is best 

 availed of when a wide area is worked; and not in small pits, con- 

 fined by perpendicular sides. The shovelling was also much easier 

 first, because the marl was more in large lumps, and less in a finely 

 reduced state than before ; and secondly and mainly, because the 

 height of the cart was the greatest extent to which it had to be 

 thrown, instead of double throwing, as before, and the throw out 

 of the pit, which at the maximum, was 13 feet in height, besides 

 the lateral distance. This change, taking away all the throwing 

 out of the pit, saved much more than one-half of the pit labour. 

 The average quantity of marl obtained before from each pit-man's 

 daily labour was 148.42 bushels. Now, one man only was usually 

 employed, who dug for the carts from 400 to 600 bushels a day. 

 It is true, that he was now relieved from assisting to load, which 

 work was put upon the drivers. In the closing operations of the 

 digging, when small pits still had to be sunk, and through the 

 bottom stony layer, and the marl from them thrown up on the 

 sloping roadway, and walls to cut down, the result of the pit-man's 

 work was much less. But even then, when the difficulty was 

 greatest, the least amount of marl obtained was 160 bushels for 

 each man in the pit. It is certain, that throughout the whole ex- 

 cavation of the range, the pit-man's labour furnished on the ave- 

 rage more than twice the quantity of marl. This part of the cost 

 then also was reduced fully one-half. But this is in advance of 

 describing the later of the operations of which the cost was so re- 

 duced. 



The digging down and removing the marl in the pit to the grade 

 of 5 to 6 feet depression in the 100 of length, served to reach tho, 



