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PB0CEEOINGS OF THE GEOLOGICAL SOCIETY. 



[Apr. 10, 



boulders piled on one another and resting on the surface of the 

 shingle. 



Terraces in California. — Before leaving these shingle-deposits 7 

 which are so largely distributed throughout the mountain-valleys 

 of British North America, I may mention that in California I found 

 these terraces ranging on the western slope of the Sierra Nevada, 

 at least to the height of 3000 feet, and there they are extensively 

 worked by the hydraulic method for the sate of the gold they con- 

 tain. At Nevada City, and also on the Yuba River, I saw deposits 

 of this shingle-conglomerate, 200 and 300 feet in thickness, ac- 

 tually being washed off from the face of the country by this power- 

 ful means, which consists in delivering water under great pressure 

 against the face of the cliff, from nozzles like those of a fire-engine. 

 The supply of water for this purpose is in the hands of companies 

 separate from those that conduct the mining, as it is often brought 

 through tunnels and over high-level aqueducts from remote and 

 uninhabited regions. The particles of g v old care disseminated through- 

 oat the whole deposit, but the richest washings are from its base, 

 where a pink pipe-clay, technically known as " pay-dirt," rests on the 

 " bed-rock." The whole water, with the material washed out of the 

 cliff, is directed through long troughs called " flumes," which are con- 

 structed of wood, like mill-leads, often continuously for six or seven 

 miles. The large stones are thrown out, as they pass, by men with 

 shovels, to save the wear on the bottom of the " flume," while the 

 finer material is carried on by the rush of water, and passes over 

 frequent crossbars called " ripples," where a little mercury is placed 

 to entrap the gold by amalgamation. At Nevada City, where the 

 coating of shingle-deposit has thus been cleared from the surface of 

 the coarse-grained and soft granite which underlies it, gigantic masses 

 were exposed on what had once been the rugged shore of an inlet, 

 just as may be seen on a waterworn coast of the same material at 

 the present day. In California fragments of wood are found 

 throughout the shingle in abundance, often carbonized, but in 

 general silieified into a substance exactly resembling asbestos. In 

 the sand and conglomerate of the Ivootanie Valley I found fragments 

 of wood of similar appearance. 



As my observations in California should not properly be introduced 

 in this paper, I shall leave them for another opportunity, the object 

 of my having mentioned them being to point out the great similarity 

 between the superficial deposits of the great gold-country and those 

 within the British territory further north, which encourages me to 

 assert that the whole country up to the Kootanie River and the base 

 of the Rocky Mountains, wherever the ancient terraces prevail resting 

 on Silurian or metamorphic rocks, will be found to be auriferous. 

 In my party in 1S59 I had an expert " washer" who had been at 

 the Californian mines ; and he frequently got " colour," as a faint 

 trace of gold is termed, by merely washing the gravel from the beds 

 of the streams, without any regular " prospecting " or " digging." 

 The discovery of what are among the richest " pan-diggings " on the 

 Pacific coast in the Sehimillcomeen Valley, and the existence of 



