Geology of Wiltshire. 325 



vation is made, as indicated by the shaded portion of the sketch, throughout 

 the whole width of the working, a distance averaging from 18 feet to 30 feet: 

 a dimension wholly dependent on the nature of the overlying stratum or 

 "ceiling," the strength of which regulates the size of opening that may be 

 worked without fear of settlement. In these quarries the roof is generally 

 very strong, and the system of commencing to excavate in the top-most member 

 of the beds, aifords an absolute security from falls. The removal of only nine 

 or ten inches of material beneath the ceiling, deprives the overlying strata of 

 siipport, as effectually as cutting away the stone from roof to floor would do ; 

 hence, should there be any tendency to settle, it is always shown at a period 

 when human life is not exposed to its influence, and when an actual drop could 

 do no possible injury to the workmen. The picking is effected by means of 

 tools shaped something like an adze, the heads of which can be shifted on to 

 longer handles as the work gets out of reach, and thus the men carry the 

 narrow hole shown in the section, a distance of about twelve feet back into the 

 rock. This completes the first process ; and an entirely new agency now comes 

 into action for the final removal of the blocks. Every one at all acquainted 

 with the Bath stone, knows that it can be readily cut up by means of an 

 ordinary saw. This is the case even after its whole substance has become 

 hardened by exposure to the air ; but it is especially so in the quarry, where 

 the stone is rendered softer by the large amount of moisture diffused throughout 

 the beds. The front elevation, fig. 2, shows a number of thickish black lines 

 extending downwards from the pick-hole to the next recurring "parting." 

 These represent saw- cuts ; and they are made by a tool differing little in shape 

 and appearance from an ordinary " cross-cut," but having a handle at one end 

 only. The position of this saw during work is shown upon the section ; and 

 no further explanation is needed to make its operation clear. After the bed 

 has been divided down to the natural joint, and the blocks thus separated from 

 the parent rock on all sides but one, levers are introduced into the parting, and 

 the whole detached by forcibly breaking off at the back, when the stone is 

 ready for immediate removal to the discharging platform. Immediately after 

 opening out a face of work, a five or ten ton crane is erected in such a manner 

 as to sweep it all over. One of these is shown in fig. 1 , fixed on bearings let 

 into both roof and floor. These cranes are ingeniously contrived to suit varia- 

 tions in headway, such as are caused by difierences in the depths of the valuable 

 beds. The post is telescopic, being capable either of sliding out to the loftiest, 

 or contracting to the lowest spcee afforded. A large expense in continual 

 alterations is thus avoided, and the periodical shifts from worked-out to new 

 localities is made without trouble or loss of time. After the blocks have been 

 loosened, a lewis bolt is let into the face of each stone at H, and the chain of 

 the crane made fast to it : one piece after another is thus dragged out, assisted 

 by the crowbars of the men, and falls to the floor, whence it is soon conveyed 

 by the trollies to the discharging platform. The next and all the remaining 

 beds are taken out by a modification of the processes which we have just 

 described. By the removal of the layer immediately below the picking-bed, 

 sufficient space is obtained to allow the workmen an entrance under the roof j 

 and figs. 3 and 4 show the manner in which they make use of this advantage. 

 Vertical cuts (g, g, g) ai-e again carried down to the next succeeding parting 



