The Rocks of Clear Lake near Sudbury. 345 
analysis of the pure pyrrhotite gave 4:22 per cent. nickel 
and 0:21 per cent. copper. 
Near the gabbro a rock occurs which, to the naked eye, 
appears to be a syenite, a flesh colored or dark yellowish 
grey rock sometimes appearing quite massive, at others 
splitting into thin plates. Under the microscope it proves 
to be a micropegmatite much like that described by Prof. 
Williams from the township of Levak,', although the 
nucleus from which the granophyre structure radiates is in 
my sections generally a crystal or group of crystals of 
plagioclase instead of a Carlsbad twin of orthoclase. 
A very similar structure is described and figured in 
photo-reproductions by Julius Romberg from South Ameri- 
can granites. He holds that the structure has been caused 
by weathering of the felspar, at times aided by the plastic- 
ity of quartz under intense pressure; as though canals 
could be formed in this way and plastic quartz forced into 
them. My specimens afford no support to such a theory 
but rather seem to show that small crystals of plagioclase 
or orthoclase or groups of crystals formed nuclei about 
which the very acid magma solidified as quartz and ortho- 
clase on all sides at once, each hampering the other and 
thus giving rise to the granophyre structure. In the 
freshest slide examined the nuclear crystals are quite sharp 
edged and unweathered in appearance. In most cases all 
the quartz and all the felspar about a given centre are 
similarly oriented, though opposite sides sometimes differ 
in this respect; and the felspar, which is unstriated as a 
rule, is not generally continuous with the central crystal. 
If the structure results from weathering or pressure, why 
should the nuclei have distinct crystalline outlines and the 
orientation be uniform in the quartz, which, if forced in 
while plastic should show irregular orientation or a chalce- 
donic structure? In some instances the quartz increases in 
amount as it runs outwards and fornis solid masses outside 
1Sudbury Mining District, p. 78. 
2 Neues Jahrbuch fiir Min. Geol., etc., VIII Beilage Band, Zweites Heft, 
1892, p. 314. 
