a 
PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 553 
In approaching postulate the third, no small difficulty presents itself at the 
outset, on account of the different views held by different authorities regarding 
the constitution of certain of the rocks named. 
In the foregoing general classification we have, on the one hand, diorite set 
down among hornblendic rock, 7.¢., those in which hornblende is associated 
with orthoclase and albite; and, in the augitic series, we have hypersthene, 
gabbro, and dolerite. 
From Cotta we learn that diorite is a compound, not of hornblende and 
albite, but of hornblende with oligoclase. The same authority gives us diabase 
as an augitic compound, with hyperite as its synonym ; while elsewhere, in the 
same work, hyperite is defined as a variety of gabbro. 
Dana distinctly states * that diorite is a compound of albite and hornblende, 
diabase t one of hornblende and labradorite ; and he seems to indicate that this 
last rock passes into hyperite. 
Professor GREEN tells us that diorite is composed of oligoclase and horn- 
blende ; that hyperite is an augitic rock resulting from the substitution of 
hypersthene for the augite of gabbro or dolerite; and he gives us anorthite as 
a component only of Corsite. 
BiscuHoF so strongly disallows the presence of either labradorite or anorthite 
in diorite, that he, in his third volume, fences with every one of the analyses of 
DELESSE, which clearly demonstrate their occurrence ; while, at page 206 of his 
second volume, he calls diorite an augitic rock which has labradorite as its felspar. 
From such a confusion as the above—which demands a congress of litholo- 
gists—we turn to the evidence of the rocks. The felspathic, as well as the 
other compound of these rocks, having been analysed in the instances which I 
shall cite, the correctness of their evidence cannot be called in question. 
Calling the hornblendic rock diorite, with what do we in Scotland find that 
hornblende associated ? 
With labradorite, in the exceptional occurrences of hornblende in the diallage 
of Balta ; with anorthite in the diorite of Fetlar; and with labradorite in the 
diorite of Portsoy, Glenbucket, Colquhanny, Deskery, and wherever it appears, 
in the long reach from the sea to the vicinity of the Dee. 
In this rock neither albite and orthoclase, on the one hand, or oligoclase, on 
the other, ever find a place. 
This association of hornblende with labradorite in diorite is exceptional, 
though not altogether unknown, DELEssE having recognised both labradorite 
and anorthite as the felspar of diorite. 
Biscuor, again, unable to get a sufficiency of lime from oligoclase to explain 
the composition of some diorites, first endeavoured to supply it by supposing 
the presence of a calcareous augite; but finally, dissatisfied with this supposition, 
* “Mineralogy,” p. 240. + Ibid. p. 343. 
VOL. XXVIII. PART II. (62; 
