554 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
concludes by saying, “there is no doubt a class of hornblendic rocks which 
contain a highly calcareous felspar.” This, in their having labradorite as 
the felspar, is precisely what all the diorites of Scotland which I have | 
examined do contain. 
Next, as to the nature of hyperite,—that is of true hyperite ; the Skye and 
Rum rock need not be considered, as the name can only be applied to it in 
virtue of a certain lithological similitude. 
In the diorite of Craig Burroch veins of hyperite, consisting of labradorite 
and hypersthene (Paulite), appear ; and the rock itself shades off into hyperite, 
both there, at Retannach, and at the Bin of Huntly. 
The mineral Paulite stands nearer to augite than to amphibole, and in 
the only localities where, so far as I know, true hyperite rock appears, it is a 
mere variety—out of many others—of a rock which has diorite as its simplest 
type—but in which a transition has been accomplished through gradual re- 
placement by augite—the intermediate mineral acting here as an intermediate 
in the lithological change. 
Here, then, the requirements of postulate third are not conformed to. My 
own opinion is, that through insensible gradations—intermediate varieties— 
augitic and hornblendic rocks pass into one another more frequently than is 
imagined. The two minerals also, in certain circumstances, are so very similar 
that I do not believe that any mode of discrimination which can be applied in 
the field, or any more expeditious than the reflective goneometer, can serve to 
determine them ; so that defective nomenclature may have been the cause of the 
drawing of too sharp a line of demarcation between the rocks which contain them. 
I have little doubt that the diorite of Portsoy, last seen in the neighbour- 
hood of Colquhanny,* will be found to shade off into the “syenite ” of Morven ; 
that the hornblendic type of rock, the augitic type of rock, the hyperitic type 
of rock, and the Biotitic type of rock occurring in the neighbourhood of Port- 
soy will come to be regarded as mere mineralogical varieties ; and that a some- 
what similar rock, occurring first about half a mile to the east of the mouth of 
the Durn of the Boyne in Banff, composed there of a foliaceous mineral— 
whether augite or hornblende the eye could not determine—and which runs up 
the country, taking a felspar as its associate, will, through several such changes, 
be found to be the northern extension of the syenite of Froster Hill. While 
it may prove to be this same belt which reappears in association with the 
serpentine of Barra Hill,—its hornblende having given way to a mixture of 
brown augite and Paulite (or bronzite), and its orthoclase to labradorite. 
A somewhat similar rock again appears at Beauty Hill, once more in 
association with serpentine ; in this there is no Paulite, and the augite is green. 
As to postulate fourth—the question whether the distinctiveness of the two 
* The belt on the Deskery may be the same. 

