232 THE AURIFEROUS GRAVELS OF THE SIERRA 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; 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 lable 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 1m- 
bedded in the detrital masses. 
