242 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
the banks of the stream to the dam at Chegwatona Lake, near the east line 
of section 27, beds of diabase and diabase-amygdaloid, with interbedded 
porphyry-conglomerates, trending N. 10° to 20° E., and dipping 60° to 75° 
south of east. The rocks, as shown by the thin sections, are in every respect 
identical with the fine-grained diabases and diabase-amygdaloids of Ke- 
weenaw Point. The following is an account, kindly furnished by Professor 
T. C. Chamberlin, of the succession displayed at this place.t His measure- 
ments were only rapid pacings, and his examinations did not begin quite so 
far down stream as the last ledges located by Mr. McKinlay. 
The locality was, however, visited after having studied in detail the adjacent 
Wisconsin formations, and the observations were made especially with reference to 
the relations of these rocks to the Wisconsin and Michigan series, and, so far as 
general structural questions are concerned, were entirely conclusive in the judgment 
of the observer. 
1. The uppermost exposure examined, 7. e., the one lowest down the river, the dip 
being eastward down stream, is a diabasic amygdaloid, much altered, con- 
taining malachite. The exposure is low and small. 
2. Ten paces up the stream, 7. e, westward, there is a similar but less amygdaloidal 
rock in low exposures. 
3. Fifteen paces further there occurs a similar rock which continues exposed for 26 
paces. 
4, This is succeeded by a conglomerate of the Keweenawan type, having a surface 
exposure of between 6 and 7 paces. 
This is followed (underlain) by about 8 paces of mixed conglomerate and amyg- 
daloid, that, for want of time, was not studied with sufficient thoroughness to 
determine its true nature. It appeared, however, to consist of the shattered 
fragments of the upper vesicular portion of a lava flow mingled by wave 
action with water-worn pebbles of more distant derivation. 
6. This is followed by about 45 paces of diabase, more or less amygdaloidal, and be- 
longing to the more common type of Keweenawan diabases. 
. This is underlain by conglomerate of the common Keweenawan sort, having a 
surface width of about 12 paces. 
. This is succeeded by diabase and amygdaloid, more or less concealed and varying 
in character, for a space of 79 paces. 
9. This is followed (underlain) by a reddish very amygdaloidal rock, which, in 6 to 7 
paces, graduates into 
10. A bed of the common Keweenawan diabase, which has a surface extent of 12 
paces. , 
11. This is succeeded by a reddish-brown amygdaloid for 10 to 12 paces. 
12. Then follows a dark-gray diabase, including red diabasic rock, for about 12 paces. 
13. This is followed for about 10 paces by amygdaloidal rock. 
14. This again by diabase for 23 paces. 
or 
=I 
io) 
'From unpublished notes, made in 1878. 
