BUILDING AND ORNAMENTAL STONES. 311 



can be wedged off which would be shattered if exposed to the risk of 

 blasting.* 



(2) GRANITE QUARRYING. 



The methods of quarrying naturally vary with the kind and quality 

 of the material to be extracted. In all the object aimed at is to obtain 

 the largest and best shaped blocks with the least outlay of time and 

 money, and this, too, so far as possible, without the aid of explosives of 

 any kind, since the sudden jar thus produced is extremely liable to de- 

 velop incipient fractures and so shatter as to ruin valuable material. 



In quarrying granite there is less to fear from the use of explosives 

 than in either sandstone or marble, while, at the same time, the greater 

 hardness of the stone renders the quarrying of it by other means a mat- 

 ter of considerable difficulty and expense. 



In the leading quarries of Maine and Massachusetts no machinery is 

 used other than the steam drill and hoisting apparatus. By means of 

 the drills a lewis t hole or a series of lewis holes is put down at proper 

 intervals to a depth dependent upon the thickness of the sheets. These 

 are then charged, not too heavily, and fired simultaneously, hi the 

 Hallo well quarries, where the sheets of granite are entirely free from 

 one another, this is all that is necessary to loosen the blocks from the 

 quarry, and they are then broken up with wedges. In many quarries, 

 however, where the sheets are thicker or the bottom joints less dis- 

 tinct, it is necessary to drill a series of horizontal holes along the line 

 where it is wished to break the rock from the bed and then complete 

 the process with wedges. 



(3) MARBLE QUARRYING. 



In quarrying marble and other soft rocks, channeling machines are 

 now largely used. These, as shown in the illustration (page 312), run 

 on narrow tracks, back and forth over the quarry bed, cutting, as they 

 go, vertical channels some 2 inches in width and from 4 to 6 feet in 

 depth. After the channels are completed a series of holes from 8 inches 

 to 2 feet apart are drilled along the bottom of the block, which is then 

 split from its bed by means of wedges. This under drilling is called 

 by quarrymen " gadding," and special machines, which are known as 

 " gadding machines, 77 have been designed for the purpose. (See fig- 

 ures on pages 325 and 326.) At the Vermont marble quarries both the 



* A good, illustration of the utility of jointed structure as an aid to quarrying sedi- 

 mentary rocks is offered in the Primordial conglomerates about Boston. These consist 

 of a greenish gray groundmass, in which are embraced a great variety of pebbles of 

 granite, quartzite, melaphyre, and felsite of all shapes and sizes. The beds are trav- 

 ersed by two series of vertical joints which cut the rock and its included pebbles, 

 granite, quartz, melaphyre, and felsite alike, with almost as sharp and clear a cut as 

 could be made by the lapidary's wheel. The joints are very abundant, and in many 

 cases quarrying would be a practical impossibility without them. Whenever smooth 

 walls are required the stone is laid on its bed with the joint face outward. 



1 1 find the word also spelled louis. For description see Glossary. 



