176 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
in the Pass of Leny, are placed at the exposed base of the whole 
series. With reference to the structure of the ground Sir A. Geikie 
remarks:—“Over many square miles the angles of inclination are low 
and the successive bands may be traced from hill to hill, across strath 
and glen, forming escarpments along the slopes and outlines on the 
summits, precisely as gently undulating beds of sandstone and lime¬ 
stone may be seen to do in the dales of Yorkshire.” In this address 
he proposes the term Dalradian for these rocks, to include the whole 
region lying to the south-east of the great glen, and the north of 
Ireland. 
In his Geological Map of Scotland, published 1892, Sir A. Geikie 
gives some of the results of the differentiation of these rocks by the 
officers of the Geological Survey, the principal additions in the map 
being the bands of graphite schist and sericite schist seen along the 
higher ridges of Loch Tay, and extending from Loch Fyne, in the 
west, into the eastern Highlands. The occurrence of two large 
faults is also marked; the one extending from Aberfoyle through 
Loch Lubnaig and Loch Tay and onwards through the higher 
reaches of Glen Tilt; the other running in a parallel direction from 
Luib, in the valley of Glen Dochart, through Glen Lochay, above the 
falls, and onwards into the eastern Highlands. This map serves to 
illustrate the succession given in the Presidential Address of 1891, 
the lower grits and greywackes being succeeded to the north by the 
mica-schists and limestones of Loch Tay, and these again in their 
turn being overlaid by the sericite and graphite schist bands of Tyn- 
drum, Craig-na-Challeich, Ben Lawers, and Ben Vrackie, while the 
whole is overlaid by the quartzites and grits of Glen Lyon, Schie- 
hallion, Blair-Atholl, etc. 
The next reference to these rocks which we have to note is that 
of Sir A. Geikie^ in the last edition of his Text Book of Geology, 
published in 1893, where he says :—“It is deserving of remark that 
the rocks along the southern margin of the Highlands are for the 
most part so little affected as closely to resemble portions of the un¬ 
altered Silurian series of the south of Scotland, and that they dip 
towards the mountains, becoming more foliated as they recede from 
the lowlands.” He also here mentions the discovery by Mr. Peach 
of radiolaria in the cherts found associated with the graphite schist 
of the southern margin of the Highlands. 
In a paper by myself,® published in the Geological Magazine 
for last year, I have arranged the clastic rocks of the southern 
Grampians in the following zones, according to their larger litho¬ 
logical features :— 
