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BULLETIN OF THE LABORATORIES 
2. Rocks having the composition of mica-diorite or diorite, but 
containing much calcite. Rocks of this group tend to assimilate 
closely in appearance and structure to the schists in contact and sug- 
gest the possibility of their having been the products of metamorphism 
•of the schists themselves again altered by slow metasomatic 
changes. A circumstance greatly favoring this theory is the fact that 
the dykes in the underlying granite are always diabases so far as ob- 
served while the diorites are very frequent in the schists. That the 
contact action of the granites was amply sufficient to produce such 
fusion is abundantly demonstrable. 
4. Orthoclase and quartz-orthoclase felsite-porphyries occurring 
under two conditions, but generally in such a way as to suggest an ex- 
traneous origin of the porphyritic ingredients ; first, contacts of con- 
glomerates with dykes of diabase or of diorite, second, interbedded 
layers in the schist with adjacent alteration and veiny structure. We 
incline to the belief that the greater part of the porphyry can be 
traced directly to metamorphism in such conglomerates induced by 
adjacent later eruptives. 
Having thus briefly disposed of the two older groups we will now 
consider the relation of the third or Keweenawan series to these. 
The direction of the strike and dip of these series on Michipicoten 
Island and Capes Choyye and Cargantua, furnish the only data on 
which to base our conclusions. The strike on Michipicoten Island 
appears to be in general a little N. of E., varying from the E. end of the 
island to the W. end, toward the west end becoming more northerly. 
At cape Choyye the strike seems to be in a direction a little W. of S., 
while at cape Cargantua it extends in almost a southern direction, va- 
rying a little to E. This would seem to indicate that the older rocks 
upon which the Keweenawan rests formed a synclinal with its axis in 
a N. E. direction. The position of the granite rocks on either side of 
this axis would indicate a synclinal rather than an eroded anticlinal, 
as is the general rule. Also the fact that the Keweenawan is deposit- 
ed within the basin itself and its margins abutt against the high cliffs 
of the eroded older rocks. The relation of the basement conglomer- 
ates exposed at cape Choyye to the older series will be discussed upon 
a later page. The most complete discussion of the Keweenawan is 
that of Prof Irving, in his monograph of the Copper-bearing 
Rocks of Lake Superior. We may now proceed at once to a 
