OF DENISON UNIVERSITY. 
139 
gree to which they have decomposed, the ingredients being exactly the 
same in the two specimens. Felsite porphyries are very numerous in 
this conglomerate, occurring in well rounded boulders. The magma 
is dark red in color, frequently showing fluidal structure. In many of 
the specimens minute grains of quartz have almost entirely replaced 
the matrix. Quartz crystals of any considerable size are rare in many 
of the specimens. Orthoclase crystals, with regular form, but much 
altered, are present in large quantities. These porphyries resemble 
closely No. 1019, already described, which occurs at Dog river, on the 
mainland. The matrix in which these boulders are imbedded varies 
greatly, according as it approaches the diabase No. 1088, which complete- 
ly covers it. Small crystals of quartz, orthoclase and plagioclase, which 
are remarkably free from alteration, calcite, together with a few small 
fragments of much altered diabase, and several other ingredients 
which could not be identified, make up the mass of the rock. 
The conglomerate which occurs at cape Choyye is made up entirely 
of loosely compacted grains, quartz and feldspar being the principal ones. 
There seems to have been no such action of heated matter at this 
point, as on the island where capped by diabase, nor do boulders of 
such size here occur. As seen from the above, the observations of Ir- 
ving, in regard to these conglomerates, do not seem here to apply. 
For as we have said, there are boulders of three distinct kinds in the 
conglomerate on Michipicoten island, which have no parallel in the 
rocks occurring there, but can be easily referred to the older Lawren- 
tion and Huronian. 
The quartz porphyries which occur about one mile south-east from 
the mines toward the center of the island appear to be closely related 
to the conglomerate described above and have all the appearances of 
being simply this congloinerate fused by the overflow of the diabase. 
Our data are too meager to make this anything more than a sugges- 
tion. A careful study of the ground and patient tracing of contact 
zones are necessary before anything can be positively affirmed of 
these. The weathering to which these rocks have been subjected, ren- 
ders the problem all the more difficult, as in many places soil several 
feet thick has been formed. 
No. 1 099 ( Plate XIII, Fig. i .) is a typical illustration of these por- 
phyries. It is of a very dark red color. Crystals of quartz and or- 
thoclase, averaging about a sixteenth of an inch in size, are regularly 
distributed throughout the specimen. The. magma is light red in color 
