46 J. S. Diller—Latest Volcanic Eruption um 
being formed by a mass of broken angular blocks of lava, and 
completely impassable to beasts of burden. The fragmental 
stony character of the lava flow resulted from its extreme vis- 
cosity at the time of the eruption. The crust was repeatedly 
broken up by the friction and pressure of the moving viscous 
lava beneath, and shoved along in such a way as to round 
some of the fragments by attrition. 
About the lava field, and extending away from it in all 
directions, for a distance of from ten to twelve miles is the 
field of volcanic ashes. It is covered with pine forest which 
has attained the maximum development for that region. Close 
to the base of the Cinder Cone the thickness of the ashes 
could not be readily ascertained. One-fourth of a mile away, 
however, they are over seven feet in depth and gradually thin 
out to the border of the field. In the immediate neighbor- 
hood of the cone a trunk of Pinus ponderosa growing directly 
upon the upper surface of the sand has a circumference of 
over twelve feet. There are numerous dead trunks of the 
same pine standing near by which were evidently killed at the 
time of the eruption. Hxcavations at the bases of these trees 
show that they extend down through the volcanic sand to the 
original soil over seven feet beneath the present surface. 
Many of the trees killed at the time of the eruption have de- 
cayed and disappeared, but their positions are marked by 
numerous pits upon the surface where the sand has slid in to 
take the place of the decayed wood. 
It is obvious that the voleanie sand of the ash field is con- 
tinuous with the material of the Cinder Cone, and that both 
are products of the same eruption, and older than the lava 
with which they are associated. The lava plainly belongs to 
two periods of effusion separated by a time-interval during 
which over six feet of infusorial earth was deposited upon 
the older portion. At the time of the final eruption, when the 
ancient lake bed was in many places raised above the present 
level of Lake Bidwell and Snag Lake was formed, tie great 
mass of the lava was quietly extravasated without any ejections © 
whatever from the Cinder Cone. 
The lava is readily recognized as basalt, one of the common- 
est of all types of late voleanic rocks. It has all the essential 
constituents of ordinary basalt, 1. e. plagioclase feldspar, augite 
and olivine together with accessory magnetite and a large pro- 
portion of unindividualized material which is generally globu- 
litic. In addition to all these characteristic constituents of 
basaltic lava this basalt is remarkably anomalous in containing 
numerous grains of quartz. 
Only four probable hypotheses suggest themselves in expla- 
nation of the origin of these quartz grains in the basalt. They 
