188 TRANSACTIONS-PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
a comparison between the volcanic phenomena of the Tertiary rocks 
of the Hebrides and the granites of the Highlands, along with the 
lavas and agglomerates of central Scotland. He shows that both 
in the Hebrides and in the southern Highlands the granites are 
seen to pass upwards into syenite-granite and felsite, and that 
“Unmistakable evidence, both stratigraphical and palaeontological, 
and of totally independent character in either case, has led us 
to the conclusion that the subaerial felstone and porphyrite lavas 
of Lome, the similar subaqueous lavas of central Scotland, and the 
intrusive masses of identical ultimate chemical composition in the 
Grampians, were all formed during the same geological periods 
—those constituting the latter part of the Palaeozoic epoch.” Prof. 
Judd then proceeds to instance the case of Ben Nevis, for which he 
claims a similar structure to the Tertiary volcanoes of the Hebrides, 
passing from a basal granite through agglomerate into a felstone 
towards the summit. 
Whether we agree with Prof. Judd or not in the reading of the 
structure of Ben Nevis, it has always seemed to us that his connect¬ 
ing of these eruptive bosses of plutonic rock with the volcanic series 
of Lome and central Scotland was a masterly generalisation, and 
the recent work of the geological survey in the south-west Highlands 
has tended to confirm this view. 
In the Government Report of the Geological Survey for the 
present year. Sir Geikie refers to Mr. Kynaston as having found 
that a group of dykes and sills of porphyrite can be seen to pass 
from the andesites of Lome across the older rocks and enter the 
Ben Cruachan granites. He also thinks that the porphyrite dykes 
and sills have a strong petrological and chemical relationship to the 
granites on the one hand and the andesites on the other. It is likely 
then that further investigation may tend to confirm the view, origi¬ 
nally propounded by Prof. Judd, that the intrusive plutonic rocks 
of the southern Highlands are but the plutonic representatives or 
roots of those volcanoes which were active during later Palaeozoic 
times, and whose volcanic products we find interbedded amongst 
the Old Red Sandstone and the Carboniferous sediments. 
We have attempted in this paper to bring before the members 
a concise view of some of the more recent advances which have 
been made in the study of the rocks of Highland Perthshire. 
Involved as they are with the general structure of the southern 
Highlands, it has been necessary for us to refer to other localities 
along the southern Grampians outside of our own county. To 
interpret the geological structure of Highland Perthshire you will 
often find it of advantage to go farther afield, and at least to extend 
your investigations to the neighbouring counties. Again, it has been 
