186 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
Again, at the head of Loch Lomond, there is a well-known example 
of an acid and a basic igneous rock associated together in one great 
intrusive mass, to which the term “plutonic complex” has been 
applied. 
Within the last few years, principally through the influence of a 
valuable paper by Messrs. J. R. Dakyns and J. J. H. Teall, published 
m the Quarterly Jourtial of the Geological Society for the year 1892, 
It has come to be recognised that the association together of these 
representatives of the two extreme types of igneous rocks cannot be 
looked upon as representing two distinct and separate acts of 
volcanic intrusion. On the contrary, they have been separated out 
from the same magma. 
Before proceeding to a notice of this paper by Messrs. Dakyns 
and Teall, we should like to draw your attention to the fact that 
these later views of the chemical segregation from the same magma 
of two extreme types of igneous rock had already been to a certain 
extent anticipated by earlier geologists. Thus we find F. Odern- 
heimer, in a paper on “The Mines and Minerals of the Bread- 
albane Highlands,”published in the year 1841, applying the 
segregation theory to account for the association together of the 
above-mentioned acid and^ basic rock seen at Tomnadashan, on 
Loch Tay. Speaking of this plutonic complex, he says;—“It is not 
very possible to ascribe a previous age to either greenstone or por¬ 
phyry; they seem to be contemporaneous, and the veins of greenstone 
in porphyry and of porpyhry in greenstone may be veins of secretion 
or an accumulation of similar masses in tabular spaces out of a mixed 
compound of minerals in a melted state. These veins of secretion do 
not require the supposition of rents and fissures of secondary origin. 
They are only the effect of an arrangement in the interior of the 
mass, perhaps caused by an electrical polarity, which may be sug¬ 
gested to exist in a compound of melted materials of different natures. 
Along with later writers upon these rocks, we had adopted the view 
that they represented two distinct periods of intrusion, though we were 
acquainted with the remarkable fact that nowhere does the granitite, 
which was supposed to be the later eruptive rock, pass out of the 
mica-diorite into the surrounding schists. Had this been the case, 
then it would have tended to favour the view of a separate intrusion 
for each rock. ^ But as the granitite does not pass out of the mica- 
diorite, we think it strongly presumptive evidence that they have 
both been segregated from the same magma.” 
In the paper we have just mentioned, by Messrs. Dakyns 
and Teall, “On the Plutonic Rocks of Garabal Hill and Meall 
Breac, published in 1892, a valuable contribution has been made 
to the study of these plutonic complexes. This locality is situated 
