768 A. P. COLEMAN 
feet in length along the offset and 50 to go feet across it, and having 
a known depth of 1,000 feet. About 700 yards west there is a narrow 
band of norite with some ore running south for about a quarter of a 
mile. After another gap of two-thirds of a mile the last outcrop of 
norite and ore occurs at the Evans mine. The whole length of the 
offset is more than 4 miles. 
It is assumed that all the isolated stretches of norite and ore are 
either connected by devious channels below the surface, or that they 
were once connected by portions that have now been eroded away. 
One band of norite and ore, that of the Frood and Stobie mines, 
is of a different kind, showing no point of attachment with the basic 
edge of the eruptive, but running for 2 miles nearly parallel with it. 
Here there is probably an underground connection with the main 
range. ‘The longest offset is from the middle of the northern range, 
running more than 6 miles to the west. : 
The basic edge of the nickel eruptive has often a very irregular 
contact with the rock beneath, frequently inclosing blocks of it and 
running short distances into it. The offsets are variable in cross- 
section, and sometimes form curious breccias with blocks of the adjoin- 
ing rocks, and also of norite of a coarser or finer grain than the matrix. 
The pyrrhotite takes its part in these relationships very much as the 
rock does, but it probably remained fluid longer than the norite and has 
penetrated more intricately into the rock beneath. Often both norite 
and rock grow finer-grained at the edge, showing that the adjoining 
rock was colder and chilled the magma in contact with it. 
The injection of the magma between the flat-lying upper rocks 
and the complex of graywacke, schist, and granite beneath occasioned 
great fracturing and crushing along the lower surface, and in some 
cases near the southern range there are numerous faults due to the 
collapse of the rock-floor when no longer supported by the magma 
which had risen from beneath it. These irregular fractures and 
faults probably afforded the channels through which the offsets 
reached their present position. 
THE UPPER CONTACT OF THE LACCOLITHIC SHEET 
The acid or upper edge of the sheet seems to have caused much 
less fracturing and fissuring of the rocks in contact with it than the 
