THE FOSSIL PLANTS. 231 
ined, would present any such difficulties as to make the assumption necessary 
that they have been ejected from the interior of the earth. In cases where 
infusoria seem to have been actually ejected from craters, as is said to have 
been the case in some of the South American volcanoes, it is not difficult to 
understand that an ancient crater may have become filled up and temporarily 
converted into a lake; and that, after the growth and deposition of an infu- 
sorial deposit at the bottom, a new eruption may have broken out in the 
same place as a previous one, or in its immediate neighborhood. In such a 
case, among the ejected material a large quantity of the infusoria would be 
found, mingled with the ashes, which must pass through the material collected 
in the bottom of the crater as they rise from the interior of the earth. The 
bursting of lakes at the bases of volcanic cones, caused by the rapid melting 
of the snows above them, have often given rise to torrents of volcanic mud, 
called “moya”’ in South America, in which both animal and vegetable re- 
mains are often enclosed in great quantity; but the connection between the 
organic and inorganic phenomena, in such cases, is perfectly evident. 
Section II. — The Fossil Plants of the Auriferous Gravel Series. 
As the fossil plants found in connection with the auriferous gravels is the 
subject of a special report, prepared by Mr. Lesquereux, and forming a portion 
of the present volume, it will not be necessary to devote any considerable 
part of this chapter to that branch of the subject. Some additional informa- 
tion, however, may with propriety be given in regard to certain points 
connected with the mode of occurrence, the distribution and the relative 
abundance of the remains of a former vegetation imbedded in the detrital 
deposits which have been described in the preceding chapter. Such general 
considerations as properly connect themselves with the climatic conditions 
prevailing at the time of the growth of the plants in question may, in accord- 
ance with the plan of this volume, be reserved for a future chapter. 
From what has been stated in the preceding pages it will have been in- 
ferred that the remains of vegetable life, in the form of trunks of trees, 
impressions of leaves, and the like, are of common occurrence in the strata 
worked by the hydraulic mining process. This is indeed the case; for from 
the most southern to the extreme northern localities mentioned, in the de- 
tailed description of the gravel region, there seem to be but few districts 
where such remains have not been noticed. ‘The material which could be 
