DETRITAL ROCKS OF THE TEMPERANCE RIVER GROUP. 327 
cent. of silica. Just where the sketch was taken the dip lakeward was 
unusually high. Further down the coast it soon flattens again. 
The rock constituting the point at Grand Marais is again all ashbed- 
diabase, though for the most part coarser-grained than that described above. 
It has a brown color, is exceedingly dense and hard, and shows a well-marked 
cross-columnar structure in places. In the thin section it is seen to contain 
much augite, both in the round particles characteristic of the ashbed-diabases, 
and indicative of relatively rapid solidification, and in particles whose con- 
tours are determined by the pre-existing plagioclases. It is thus a well- 
marked intermediate stage between the diabases of the ordinary type and 
of the ashbed type. Besides the tabular plagioclases of the matrix there are 
also present larger porphyritic plagioclases. 
The strong resistant power of this rock is shown in the existence of 
such an exposed ledge as that which forms the protecting reef of Grand 
Marais Harbor. The rock is in part more dense than that represented by 
the above description, and, to judge from the numerous angular fragments 
on the shingle ridge forming the east side of Grand Marais, must graduate 
downwards into an aphanitic diabase-porphyrite. 
The detrital rocks of the Temperance River Group were noticed at 
several points along the coast. The westernmost of these is in the N. E. 
4, Sec. 11, T. 56, R. 7 W., where a thin seam of red shale, with very irregu- 
lar thickness, holds balls and fragments of amygdaloid, and occasionally has 
amygdaloidal material strangely mixed up with the red sand of the matrix. 
This seam overlies a porphyritic amygdaloid, which graduates downward 
‘nto a true ashbed-diabase, and is overlain by an excessively vesicular thin 
amygdaloid. The whole occurrence, then, is an exact repetition of the 
ashbed of Keweenaw Point, the same peculiar dense diabase being fur- 
nished with the same peculiar scoriaceous amygdaloid. What appears to 
be the conglomerate just mentioned, but thickened, is seen in a vertical 
wall 36 feet high at the bottom of a bay in the extreme northeast corner of 
section 11. The overlying and underlying rocks are not seen here, but at 
its eastern extremity this conglomerate comes into abrupt vertical contact 
(the contact being seen on a wall 30 feet high) with a dark brownish-gray, 
fine-grained rock. This rock the thin section shows to be a typical luster- 
