ACADEMY OF NATURAL SCIENCES. 389 



known to have taken place in the Sierras witfiin the most recent geological 

 periods," and the whole of which, in this case, must also have belonged to the 

 inverted portion of the strata — unless indeed the inversion were produced by a 

 peculiar sliding and bending of the strata by their own weight, the upper flex- 

 ure having been since entirely removed — and when, iu addition to this we con- 

 sider the hundreds of miles in length, and the great thickness of the strata in 

 question, we can perhaps begin to appreciate the magnitude of the movements 

 and forces which would be involved in producing such an effect. It would 

 indeed, if true, be a striking illustration of the grandeur of the scale upon which 

 many of the physical features of this country have been cast, as compared with 

 those of other and better known regions. But it is hardly worth while to 

 speculate further upon probabilities like this in the present state of our knowl- 

 edge, and I return to my subject. 



In SaH Spring Valley, the rocks consist almost entirely of slates, with little va- 

 riety of character, generally thiu-bedded, fine-grained and argillaceous, sometimes 

 magnesian or chloritic, and often splitting with facility into very thin sheets. 

 The thinnest bedded varieties are usually fragile, and the structure is often wavy ; 

 but sometimes the cleavage is regular and thin enough, and the rock possesses 

 sufficient strength to furnish a tolerable material for roofing purposes ; although 

 no attempts have been made, so far as I know, to thus apply it ; — and, in fact, 

 the expense attendant upon its excavation and transportation would preclude 

 any extensive use of it, even if its quality were unsurpassed, which it is not. 



The earthy covering of the rocks throughout the valley is usually very shal- 

 low and the soil poor, (Tower's ranch is, however, an exception) and in many 

 places the thin sharp edges of the slates project in such a way as to form an 

 exceedingly jagged surface, though the projections are low, generally not exceed- 

 ing two or three feet in height. Much of the surface is strewn with float quartz, 

 usually in the shape of small but partially rounded pebbles. Quartz veins of 

 small or moderate size, parallel with the stratification, are not uncommon. 

 Iron pyrites is of frequent occurrence, with a little gold in the quartz. Some 

 of the veins have been more or less worked, but none of them to any great extent. 

 About three or four miles westerly from Copperopolis, in the hilly portion of 

 the valley, is a ten-stamp quartz mill, and a short distance from this, on Little- 

 johu's Creek, is the site of an older one, which was burned down. Neither of 

 these mills ever yielded much profit, so far as I can learn, nor does the present 

 one seem likely to do so. 



Several of the gulches in this vicinity are said to have yielded gold enough in 

 the past to pay for working, although the diggings were not rich or extensive. 

 It is stated also that some years since, in one of these gulches, a quartz boulder 

 was found, weighing about one hundred pounds, Avhich yielded between two 

 and three thousand dollars' worth of gold. There are three or four quartz 

 veins near here, from which more or less rock has been crushed. Portions of 

 the rock from one of these veins, the Wiunemucca, a prettily-shaped vein of 

 three to four feet in thickness, are very cellular in structure, and some of it 

 shows fine gold quite freely to the naked eye. The metal however, must be 

 very irregular in its distribution, or the ore would have paid better in the mill 



