144 Tlic Auicrican Geologist. March, isy« 
E. \ Sec. I, T. 2)^ N., R. 19 W., exhibited the porphyritic 
phase developed to an unusual degree. The phenocrysts con- 
stitute nearly one-half the total bulk of the rock. On weath- 
ered surfaces these feldspars are much altered, the resultant 
products being chiefly kaolin, quartz, chlorite and epidote. 
No constant structural relation seems to obtain, although the 
higher and later flows exhibit a greater tendency to the por- 
phyritic development than do others. 
Aiuygdaloidal Diabase. The amygdaloidal zones are 
not well developed in this area. Excessive alterations in the 
upper portions of the several flows has apparently destroyed 
^ny amygdaloidal structures which may have been present. 
Pumpelly and Irving have noted jn the rocks of the Kewee- 
naw series* a similar condition. In a few cases, however, 
the true amygdaloidal character is beyond question, and man)^ 
boulders of the conglomerate are also true amygdaloids. The 
minerals filling the amygdules are chiefly quartz, chlorite and 
epidote. 
The pseudo-amygdaloid f is the most extensive alteration 
development in these rocks. Chlorite is the first and most 
common product, while quartz, e]3iclote, calcite and feldspar 
are abundant in varying quantities. 
Seliistose Stnieture in the Diabase. Locally and notabl}' 
within the village of Taylor's Falls occur limited areas of a 
grayish blue tough rock which exhibits schistose structure. 
The rock is confined to the separation zones between the 
flows, and in one instance it is in contact with an enclosed 
fragmental bed. A specimen taken from above the boat 
landing at Taylor's Falls, at the contact between the pot-hole 
bench and the base of the overlying flow exhibits crumpling 
to a limited extent. 
Flozvage. In places a wav)' banding parallel to the 
general trend of the flow is readily observed. Locally this 
banding is evident in the completely altered phases of the 
rock, while at other places the structure is more conspicuous 
in the fresher and more finely crystalline diabase. This struc- 
*Geology of Wisconsin, vol. Ill, 1880, p. z^- 
U. S. Geol. Survey, Monograph V, 1884, p. 136. 
tPumpelly: Metasomatic Development of the Copper Bearing 
Rocks of Lake Superior. Proc. Am. Acad. Arts and Sciences, vol. 
XIII, 1878, p. 268, 
