176 T. S. Hunt on Lithology. 
in rounded crystalline masses or imperfect crystals from one 
tenth to one half an inch in diameter, associated with a white or 
greenish-white crystalline feldspar, black augite, a little brown 
The proportion of olivine is very variable, but in some parts 
it is the predominant mineral. Its color is olive-green, passing 
A little silica is however retained in solution, and is precipitated 
ammonia with the oxyd of iron. Two analyses of different 
Site SS - 87°18 37°17 = oxygen 19°82 
esia, - - - - - 39°36 te SS 15:87 
Protoxyd of iron, - - 2c. Oh oie se 5:10 
99°06 99°39 
The augite of this olivinitic dolerite appears in the form of 
small crystalline grains, and also in short thick and terminated 
prisms, which are readily detached from their matrix. They 
are often an inch in length by half an inch in diameter, and are 
sometimes partially coated by a film of brown mica. These 
crystals cleave readily, presenting brilliant surfaces, and are black 
in color, with an ash-gray streak. Their hardness is 6°0, an 
their specific gravity 8°34. Analysis gave as follows: 
Silica, - - 49-40 
Alumina, - - - - . = fe z Z - 670 
Daa, ere ee ee oe ee es 
Math er ee ee eee 
Protoxyd of iron, = - Pe « = . : : 783 
da and traces of potash, - - - eo: . oe 
Volatile, - - - - = ze ‘ ‘ é “50 
100711 
The augite which abounds in the non-olivinitic dolerite, which 
forms the greater part of Montarville, does not appear to differ 
from that just described. ; 
An average specimen of this olivinitic dolerite, or peridotite, 
‘was reduced to powder; it did not effervesce with nitric acid, 
and when ignited lost only 0°5 per cent. When gently warmed 
- with sulphuric acid, the olivine was readily decomposed, with 
the separation of floceulent silica; and by the subsequent use’ 
a dilute solution of soda, followed by chlorhydric acid, and & 
second treatment with the alkaline ley, 55°0 per cent of 
