316 The Americcm Geologist. May. isos 
While making a geological map of the Knoxville district for 
Dr. Becker about eight j'ears ago the writer found conglomerates 
in the Knoxville beds at several points. A collection was made 
of the pebbles and matrices of these conglomerates, which speci- 
mens have been recently' re-examined by the writer with the aid 
of thin sections. 
One of these conglomerate beds lies about two and a half miles 
southeast of the furnaces of the Reed quicksilver mine, just north 
of the basalt area. The matrix of this conglomerate (No. 75, Knox- 
ville collection) is a tuffaceous* sandstone containing well preserved 
specimens of Aucella, so that its age is certain. It is composed 
of fragments of augite, quartz and a little hornblende, with chlorite, 
calcite and serpentine present as decomposition products. There 
are also numerous raicrolitic igneous fragments, which frequently 
contain larger crystals of augite and plagioclase and are evidently 
of the porphyrite series. Some other rounded fragments seemed 
to be phthanite. Augite is so abundant in the rock as seen 
in thin section that it might almost be called a diabase-tuff. 
This rock seems likely to have been formed from material derived 
chiefly from the secular disintegration of rocks of the diabase ser- 
ies. One of the larger pebbles imbedded in this matrix is a dia- 
base-tuff; another is a typical porphyrite, with idiomorphic plagio- 
clase phenocrysts. 
Some conglomerate collected about 650 feet northeast of 
the last localit}- is composed largely of small pebbles of fine-grained 
siliceous rocks apparently indistinguishable from phthanite and, 
like that rock, cut by numerous minute quartz veins. 
At the point called Chaparral Station on the geological mapt of 
the district occurs a coarse conglomerate containing pebbles of 
quartz-porphj'rite, and of a granular rock composed chiefly of 
feldspar and quartz. 
The exposures at Knoxville are excellent and a thorough study 
of these conglomerates and of the metamorphic rocks there ought 
to determine the question whether or not the metamorphic 
series is older. Certainly the facts given above seem to prove 
that the phthanite and diabases are older than the Knoxville 
beds. ^^^ 
*Thls adjective being derived from tuff should obviously be spelled 
with two f's and thus distinguished from tufaceous, which is derived 
from txifa. 
fSee the atlas accompanying Becker's Quicksilver Deposits. 
