40 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
physical change has been outlined with but the scantiest reference 
to its activity. The following papers will build up the life-history of 
the river in the past, and show its part in forming and modifying the 
system of slopes and surfaces, and in preparing the land for the 
reception of the flora and fauna which now inhabit it, and their 
reaction upon its water supply and movements. 
2 .—GEOLOGY. 
A.—S TRATIGRAPHICAL. 
By H. Coates, F.R.S.E. 
The River Tay, during its course from Loch Tay to Invergowrie, 
passes over two of the geological formations represented in Scotland, 
exclusive of the recent deposits which overlie these. The first part 
of its course, from Kenmore to a point two miles below Dunkeld 
Bridge, comprising about 25 miles, passes over the crystalline and 
schistose rocks of the Grampian Highlands, recently grouped under 
the name of Dalradian, but better known as the “ Highland Meta- 
morphic Series.” The lower part of its course, namely, that from 
the point two miles below Dunkeld Bridge to Invergowrie, a distance 
of about 40 miles, passes over the Old Red Sandstone. 
Of the former or Highland group, two or three members are met 
with. From Loch Tay down to Dalguise Station we pass over a 
pretty uniform stretch of mica-schist. This mica-schist forms part of 
a well defined band which runs from Glen Clova on the north-east to 
Glen Falloch on the south-west. Next we come to the band of Grit 
and Greywacke which forms the south-eastern flank of the Grampians. 
This band the river traverses from Dalguise to Dunkeld. Lastly, 
about a mile below Dunkeld, it reaches the curiously narrow strip of 
clay-slate which crops out along, or near, the south-eastern boundary 
of the Highland rocks, in a nearly uninterrupted line from Stone¬ 
haven to Port Bannatyne, in the island of Bute. This band, where 
the Tay crosses it below Dunkeld, is only about a quarter of a mile 
wide. 
Passing next to the lower section of the Tay, from Dunkeld to 
Invergowrie, we find that in these forty miles it passes in turn all the 
different members of the Old Red Sandstone series which are repre¬ 
sented in Perthshire. First in order is the Great Conglomerate, 
forming the base of the system, which extends from the boundary of 
the Highland rocks to Caputh Bridge. Here the river enters upon 
the broad plain of Strathmore, occupied by the sandstone series which 
is the most extensive member of the Lower Old Red. At Stormont- 
