514 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Concerning the lithological nature of the rock itself, there has, in the past, 
been considerable difference of opinion. 
By most writers it has been described under the vague name of “ primitive 
greenstone.” 
It found its way into many collections, from the stores of a local mmeralogist 
who termed it “ Norwegian hornblende.” Hay CunnincHAME* describes it 
particularly under the name of syenite ; and, in his geological map of Banffshire, 
jays it down as occurring of a width of about seven miles in the north of that 
county ; and as stretching, with an average width of three miles, for a distance 
of about fourteen, southward,—until in fact it reaches the Isla, the boundary of 
the county in that district. 
Though, from the covered nature of the ground, it is impossible by actual 
determination to prove so great or so continuous an extent, still I am prepared 
to admit these limits in a general way ; though I do not regard it as one single 
mass. 
The first point I would direct attention to, as regards the rock occurring 
within the limits assigned to it by CUNNINGHAME, is that it occurs therein pre- 
senting such differences in type, that I do not think that any lithologist who 
had not studied it by the convincing process of slow pedestrian exploration, 
could be brought to believe that its very characteristic varieties could possibly 
belong to one and the same substance. 
Having so done, I agree with CUNNINGHAME that all that is visible within 
the boundaries above assigned, is to be referred to one and the same general 
species of rock ; and having, after doubts and difficulties, had to admit so much, 
I have to maintain that rocks, extending far beyond the limits of CUNNINGHAME’ 
survey, must be referred to the same mass also. Such an extension is almost 
demonstrable as far as Colquhanny in Strathdon. 
The conclusions and admissions, above referred to, have been arrived at 
chiefly through having been able to trace the gradual passage of the one 
variety into the other; and also through having to maintain that, although 
the eatreme varieties depart to so signal an extent from the typical as to leave 
some room for doubt, there is yet no other known rock to which they can, 
with so great a degree of consistency, be referred. 
The constitution of the rock at its extreme north-westerly limit has been 
given ; in appearance it may be said to be a very dark brown, hackly-fractured 
rock. . 
Cotta would define it, probably, as porphyritic diorite. CUNNINGHAME terms 

it “large granular.” The hornblende is in great excess; the imbedded crystals | 
of labradorite have little effect in lightening their colour, through the deadening 
effect of their dark setting. The rock as a whole in fact is almost black. 
* “Trans, Highland Soe.” vol. xiv. 
