146 The American Geologist. Maicii, i8iis 
Associated with the breccia is a volcanic tuff. Together 
these fragmental rocks are proof of the existence of a series of 
successive lava flows in this geographic division of the Kewee- 
nawan of the Lake Superior basin. 
The ]^olcanic Tiijf. A fragmental rock of varying degrees 
of coarseness has been found in place between several of the 
flows in the village of Taylor's Falls. Near the intersection of 
Government and West streets occurs the most extensive de- 
velopment of this type of rock. Together with the breccia 
which accompanies it there is a total thickness of about twen- 
ty feet at this one point. No differences from the ordinary 
diabase are readily noticed at a little distance, for the same 
hardness and colors and surface contours prevail in this as in 
other portions of the outcrop. At no other place, however, 
is the fragmental nature of beds corresponding to this so 
easily recognized. It is in so small amount between most of 
the flows as to readily escape observation until a knowledge 
of the rock structure of the district obtained from other data 
is made use of in scrutinizing the most favorable points. Upon 
closer inspection the clastic character cannot escape notice. 
The individual particles vary in size from mere dust to the 
size of an ordinary sand grain, and in the amount of abrasion 
to which they have been su1)jected from roughly angular to 
beautifully rounded grains. The upper portion of the bed 
is stratified and the banding due to water sorting is appar- 
ent in many specimens. By the aid of the microscope it is 
observed that these individual grains are now altered to 
quartz, epidote, chlorite, actinolite and similar secondary pro- 
ducts in varying degrees. Many grains have therefore en- 
tirely lost their original characters, but in most cases it is 
probable that the original form of the grain is fairly well pre- 
served. Many grains show all the characters of a fine- 
grained diabase. These were fragments broken from adjacent 
rocks. ( )thers show flowage and devitrification indicating 
a more glassy nature. While still others retain nothing of 
their original character and seem to have invited rapid and 
complete alteration to the obliteration of everything except 
external form. These are now most commonly represented 
by quartz grains penetrated by actinolite needles, or by epi- 
dote, or a mixture of epidote and quartz, or by epidote and 
