212 The American Geologist. October, iH<r. 
to ashen gray. Tiie}'^ separate rather easily into j)arallel 
layers which have the iisnal clip of the surrounding rocks, 
into the lake(i. e., south southeast) at a low angle, although 
occasionally this angle increases to 40 degrees or even more 
and there are also local deviations in the direction of the 
dip. In the vicinity toward the w^est occur gabbro and red 
granites, while the surface rocks with which these tufaceous 
rocks are immediately associated are diabases, diabase por- 
phyrytes and basalts which are frequently araygdaloidal, and 
aporhyolytes; and they are sometimes cut by diabase dikes. 
As a rule, these tutfs are quite tine grained, the ditferent par- 
ticles being usually less than an eighth of an inch in diameter, 
and their origin is not clear except whqn studied in sections. 
Accordingly the salient features of some of these sections are 
here given. 
No. 17 is composed of small fragments surrounded by a 
matrix of very fine grain consisting of quartz, feldspar, 
chlorite, epidote, calcite and iron ore. all of which are 
secondary grains and not original fragments. The fragments, 
which are the peculiar feature of the section, are of all 
shapes, from roughly rounded and oblong forms to those 
which are jagged and very irregular in outline. They are 
usually surrounded by a rim of minute iron ore granules 
which render the outline of the fragments very distinct. 
Many of the fragments are vesicular, having one or more 
rounded vesicles whose sides are also surrounded by granules 
of iron ore. The interior of the fragments is a confused 
mass of small grains and flakes, which are principally chlorite, 
with epidote, quartz and iron ore. It seems impossible to 
reach any conclusion other than that these fragments are 
pieces of vesicular volcanic material, probably originally 
glassy but now devitrified. 
No. 61 is composed mostly of small, closely crowded grains 
which are largely rounded or subangular. These grains are 
chiefly of three kinds: (1) greenish grains, (2) feldspar, 
and (3) quartz, the last not being as common as the other 
two. The greenish grains are usually composed of minute 
flakes of chlorite and a micaceous mineral, probably sericite. 
with some quartz. Other grains are composed of an aggre- 
gate of minute grains of quartz and feldspar, the former 
