58 THOMAS COMMERFORD MARTIN 



The gold bearing placer soil of California has a depth of 

 from 10 to 50 feet, being a gravel deposit left in the old river 

 channels. After one or two holes have been put down by 

 drills, for test purposes, and an analysis of gold bearing soil 

 made, the dredges are put to work, should conditions warrant 

 it. Two types of electric dredges are used to secure the gravel 

 for treatment. In one method the gravel is lifted through 

 centrifugal pumps, while in the other — the method more 

 generally used — it is handled by an endless chain of buckets. 



The method of operation is very interesting. A boat is 

 built in the basin or excavation where the operations are 

 to be carried on, the necessary equipment is put on board, 

 and the hole is then filled with water to a depth of from 25 

 to 40 feet. Current is brought to the operating motors on 

 the boat by means of overhead wires and cables, the cable 

 being usually run out from 400 to 500 feet from the shore. 

 As a general thing, the current used is high pressure, alter- 

 nating 2 or 3 phase, and the transformers for receiving it 

 and stepping it down for use, although sometimes put on the 

 boat, are generally placed on the bank, on a pole, or in a small 

 substation. The dredge digs its own channel ahead of it, 

 depositing behind it the soil which has been worked over. 

 It may thus be said to carry its own pool with it as the work 

 shifts from point to point. The gravel is elevated into a 

 grizzly, or similar device, where the rocks are washed out 

 of the soil and delivered to the carrier, which deposits them 

 on the dump behind the dredger. The fine soil is next washed 

 through shakers and riffles, the gold being deposited on saving 

 tables, to be taken up with quicksilver, while the worked 

 over soil is deposited at the stern of the boat with the other 

 residue. 



Some idea of the character of the work may be formed 

 from the equipment of the chain bucket dredge operated 

 by the Butte Gold Dredging company. This dredge, which 

 has a draft of 5 feet and is about 36 by 90 feet on the water 

 line, is fitted with two spuds, each 50 feet long ; one, of wood, 

 weighing about 10 tons, and the other, of steel, weighing 

 about 17 tons. The swing permits of a cut about 90 feet in 

 width. There are 85 buckets to the chain, each bucket having 



