188 7] Geology and Paleontology. 655 
interesting instance of the formation of a porphyry from the 
fusion of the schist-conglomerate by contact action of a diabase- 
aphanite or porphyrite is noted. In what may be assumed to 
be the centre of the fold are great beds of calcareous gneiss, 
often with sillimanite (?) needles. These are the only stratified 
granitic rocks seen, and form an integral part of the schist series. 
Dykes of diorite are very frequent in the schist, and in every 
case assimilate the adjacent schist to them very closely in 
general appearance, though the microscopic character may be 
quite markedly different. The method of occurrence suggests 
that the diorites are really but fused portions of the schists 
pressed up through the pasty yielding schist, which thus is 
greatly affected by the contact. The diabases, on the other 
hand, are of a much later origin, and perforate the granite as 
well as the schist. The felsite-porphyries are thought possibly 
to have been formed from the injection of matter from the 
granite below at the same time at which the diorites were formed 
and before some subsequent metamorphism, which involves the 
schist and all its intrusives except the diabases. A curious mod- 
, ification of some of the diorites is described, by which the long 
twins of actinolite have lost their pleochroism completely, 
although still preserving the normal angle of the optical to the 
crystallographic axis. The hornblende becomes exceedingly like 
augite in appearance and polarization. Much that has been 
called diorite-slate and diabase-schist, when carefully studied, 
can be analyzed into various intrusive diorites, closely assimilated 
to intervening beds of mica, and hornblendic-schist or a cherty 
Keweenaw series, which laps upon the eastern shore of Michi- 
picoten Bay, is thought to occupy an original synclinal, though 
great erosion must have preceded the formation of the con- 
glomerates which are the lowest members visible. On the island 
of Michipicoten these conglomerates are well exposed, and a 
careful study of their pebbles shows that they can all be referred 
to some one or other of the formations now visible along the 
north shore of the lake. The same granites, felsites, schists, 
and diorites can be identified. Chemical analysis does not detect 
copper in any part of the conglomerate studied, but everything 
seems to point to its origin from the amygdaloids, which every- 
_ where cap the conglomerate and have in some places greatly 
metamorphosed the latter. Indeed, the writers of the paper in- 
cline to believe that some or all of the peculiar ferrugineous 
quartz-porphyry, forming the only acid eruptive seen upon the 
island, may be the result of ‘such metamorphism of the conglo- 
-Merate, Space does not permit a more extended reference to 
the interesting intrusives of the Keweenaw series, which deserve 
a careful and critical study. Microscopic sections of the rocks 
_. described are offered for exchange. © . : 
