416 Scientific Intelligence. 



As I have mentioned, the prevailing rock of the gold region near the 

 Rio de los Americanos is slate. There are many varieties of it — some 

 shaly and friable, others hard and massive, somewhat resembling green- 

 stone. The laminae of the slate beds are nearly perpendicular, and 

 their direction about N.N.VV. and S.S.E., or nearly the same as the 

 direction of the range. These slate beds often include dykes or beds 

 of quartz rock several feet in thickness. At the dry diggings above 

 named, I passed at right angles over the upturned edge of continuous 

 strata of slate a distance of four or five miles ; and in the same direc- 

 tion, slate beds occur several miles farther on, but I had not the means 

 of knowing that they were a part of the same great deposit. 



In some of the richest explorations yet made, this slate formation 

 immediately underlies the stratum of drift or diluvium which contains 

 the gold, and much of the gold is found in the crevices of the slate, 

 the rough edges of the upturned strata forming innumerable recepta- 

 cles or "pockets" as they are called, into which the metal has origin- 

 ally found its way, from its own gravity assisted by aqueous agency. 

 It is this accidental association of the gold with the slate rocks which 

 has caused the statement to be frequently made, even by persons of 

 much general intelligence, that the gold exists in the body of the rock 

 itself, and forms a component part of it, in the same sense that iron 

 pyrites forms a part of the rocks in which it occurs. But I have no- 

 where seen gold among the slate, except in circumstances where its 

 presence could be accounted for by its introduction from without, a 

 close scrutiny readily discovering some cleft or opening through which 

 it might have entered. The richest of these u pockets" are in the 

 bottoms of sharp ravines which seem to have been notched into the 

 body of the slate, and generally in situations where the bottom of the 

 ravine, after descending at a considerable inclination for some distance, 

 becomes more nearly horizontal. Just below a sudden descent or preci- 

 pice, in the bottom of a dry ravine, gold is often found in the cavities 

 in great abundance. From such a spot Mr. Douglass extracted a pound 

 of gold in a few hours, even after the place had been previously "dug 

 out/' as was supposed, and abandoned. 



I have noticed in published accounts, many erroneous statements re- 

 specting the geological position of the gold. Some have said there is 

 no particular formation in which the gold occurs — but that in different 

 places it is found in different kinds of earth or rock. You will not 

 need to be informed that this is without foundation. So far as I have 



■ 



been able to examine, or can learn from competent witnesses, there is 

 but one geological formation with which the gold of the Sierra Nevada 

 is associated and in which it uniformly occurs. This is the stratum or 

 drift or diluvium, composed of a heterogeneous mixture of clay, sand, 

 gravel, and pebbles, and varying in thickness from a few inches to sev- 

 eral feet. Here, as elsewhere, this stratum is neither horizontal nor 

 of uniform slope, but conformed to the varying inclination of the earth s 

 surface, covering the declivities, and even the summits of the hills, as 

 well as the bottoms of the ravines and valleys. Out of this stratum 1 have 

 no where found gold, except where a stream has cut it away and made 

 its contents a part of some alluvial formation of comparatively modern 

 date. The sandbars of some of the mountain torrents, and the grav- 



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