7606 A. P. COLEMAN 
made, even the hypersthene showing little or no trace of rearrange- 
ment. The association of the pyrrhotite and chalcopyrite with the 
ordinary rock-forming minerals is a matter of some interest, so that 
the relationships of the two kinds of material in the freshest sections 
will be described. 
The pyrrhotite and chalcopyrite occur generally together, the first 
being the more common of the two, and they often form sharp-edged 
masses of a round or angular shape completely inclosed in silicates. 
They most commonly accompany biotite, which may form a fringe 
around them, but are rather often found in hypersthene also. In 
many cases the sulphides lie beside solid portions of magnetite, and 
in one slide magnetite incloses pyrrhotite. 
In the freshest sections there is no hint of a splitting-up or decom- 
position of the silicates inclosing sulphides, and no visible channel 
by which the sulphides could arrive at their present position. The 
edges of the hypersthene prisms are often as square and sharp 
against pyrrhotite as against any of the silicates of the rock, and the 
whole appearance suggests a nearly contemporaneous origin of sul- 
phides, oxides, and silicates, the more basic minerals generally keep- 
ing together. 
In the dikelike offsets from the basic edge of the sheet norite and 
ore are found mixed, the rock having the same general character as 
the main range, though finer-grained and more greatly weathered. 
The intermediate stages between norite and micropegmatite con- 
sist of mixtures of the constituents of the two rocks, but the hyper- 
sthene is generally replaced by hornblende. 
The acid phase of the sheet is quite variable, but always contains 
intergrowths of quartz and feldspar. The feldspars include ortho- 
clase and also plagioclases such as andesine, while the dark minerals 
are hornblende, biotite, and some magnetite, but no pyrrhotite. The 
micropegmatitic structure ranges from very coarse intergrowths to 
almost submicroscopic varieties, where a small, sharply outlined 
crystal of andesine is inclosed in a wide border of plumy intergrowths 
in which the character of the feldspar cannot be determined even 
by high powers of the microscope. The feldspars of the acid edge 
are often platy, giving a hint of trachytic structure, as, for instance, 
near Onaping. In other cases the rock is more granitoid-looking; 
