T. S. Hunt on Lithology. 175 
exists in the form of protoxyd, and in the second specimen, in 
Part as a sulphuret. These rocks, which appear to have the 
composition of mixtures of a basic feldspar with pyroxene, do 
not differ from ordinary dolerite. 
resembling somewhat the preceding. It contains small brilliant 
black grains of ilmenite, with others of sphene, and sm 
will be successively noticed. fang 
Montarville_The greater part of Montarville is composed of 
a Coarse-grained granitoid dolerite, in which black cleavable 
augite predominates,—sometimes almost to the exclusion of any 
other mineral. Small portions of white feldspar, and scales of 
rown mica, are sparsely scattered through the rock, with grains 
of carbonate of lime. The removal of these by solution from the 
Weathered surface often gives to it a pitted character. In other 
cabal the feldspathic element predominates, and the rock 
Comes porphyritic from the presence of large crystals of augite. 
The worn surfaces of the dolerite sometimes show alternations 
this variety with another which is finer grained and whiter. 
€ two are arranged in bands, whose varying thickness and 
curving lines suggest the notion that they have been produ 
by the flow and the partial commingling of two semi-fluid masses. 
other and a remarkable variety of dolerite, found at Mon- 
‘arville, appears to be confined to a bill on the shore of a little 
lake about half a mile northward from the manor house. The 
Whole of this hill, with the exception of some adherent mections 
i hal to be composed of a granitoid dolerite, 
Containing a large proportion of olivine. This mineral occurs 
