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232 



THE ATJEIFEROUS GRAVELS OF THE SIEEEA NEVADA. 



placed in the hands of Mr. Lesquereux for description was, however, but 

 meagre, in comparison with what might have been obtained, had it been 

 possible to give the necessary time and labor to the collection and preserva- 

 tion of specimens in this department. In the first place, however, it should 

 be mentioned that a very considerable number of excellent specimens were 

 collected during the early years of the Geological Survey, and that most of 

 them were destroyed by the fire which in 1865 consumed a large part of the 

 material which had been gathered up to that time. There were other diffi- 

 culties, however, in the way of procuring satisfactory suites of specimens 

 even at localities where plant remains were abundant in the rocks. Every- 

 thing passing through the sluices is, of course, broken up and destroyed j so 

 that, in places where the hydraulic process is exclusively employed, it could 

 not be expected that anything should be preserved except fragments of wood 

 and trunks of trees too large to be handled by that method. Hence, most 

 of our fine specimens were obtained at specially favorable localities, where 

 tunnel mining was chiefly practised, and where the material excavated was 

 brought out in cars and dumped on the surface before being thrown into the 

 sluices. But even in such places it was usually necessary to be on the spot 

 at the time the mining work was actually going on in order to procure valu- 

 able material, because the fine clays in which the delicate and perfectly 

 preserved leaves are almost exclusively imbedded are liable to swell up and 

 disintegrate rapidly on being exposed to the air. It was generally necessary 

 to soak the specimens in glue or gum and cover them with varnish, without 

 any delay, or they would soon be destroyed. This was the case particularly 

 at the very prolific localities under the Tuolumne Table Mountain, and this 

 was done with a large number of specimens, which unfortunately were de- 

 stroyed, as mentioned above. Thanks to the zeal and patience of Mr. C. D. 

 Voy, a fine suite was obtained some years later from the Chalk Bluffs, near 

 Red Dog and You Bet, and these form the bulk of the material examined. 



There is no limit to the amount of fossil wood which can be obtained in 

 the various hydraulic mines of the gravel region. But it was not supposed 

 that much valuable information could be obtained from the examination of 

 the wood itself, especially when leaves, and even fruit, were comparatively 

 abundant ; hence no attempt was made to collect fossilized wood for any pur- 

 pose, except to throw light on the manner in which such material has been 

 preserved and the changes it has gone through subsequent to its being im- 

 bedded in the detrital masses. 





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