172 TRANSACTIONS-PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
that both formations are nearly vertical, but have still a southerly 
dip. At Callander a reversal of the dip is noted, and now both 
formations dip to the north, which would make the mica-schists 
overlie the clay-slates. At Comrie he says they are unconform- 
able, while at Dunkeld, Blairgowrie, and onwards towards the 
east, they are seen to dip inwards upon the mountain chain. Thus, 
in the eastern part of the mountain chain the clay-slates, grits, grey- 
wackes and mica-slates seem all to dip towards the north, so that 
the mica-slates are upon the higher horizon, while at the western end 
of the chain all these rocks, which show every evidence of being 
physically the same series, dip outwards from the mountain chain 
and towards the south, the consequence being that the clay-slates 
must be looked upon as occupying the higher horizon. The following 
is in his own words the conclusion which he arrives at:_“ The 
analogy of other localities leads us to believe that the clay-slate is the 
higher ano newer formation, and the lower inclination and more 
regular dip of the beds in Bute and on the Gareloch confirm the 
view that the strata are there in their normal position. The reversed 
position, therefore, seen at Callander and other points to the north¬ 
east, must be abnormal. He then proceeds to show how this reversal 
of the beds has been accomplished, but this we will pass over in the 
meantime. 
We now come to a consideration of those sections which deal with 
the relationships of the central gneiss and quartzites to the mica- 
schists. Nicol mentions that as far back as the Leeds meeting of the 
British Association in 1858 he held that the great central formation 
of gneiss, quartzite, and limestone of the southern Grampians must 
overlie and be younger than the mica-schists. In a footnote he refers 
to the recently-published map of Murchison and Geikie, as also 
showing that the gneiss, quartzites, and limestones of Glen Lyon, 
Blair-Atholl, Schiehallion, and Ben-y-Ghloe belong to a lower 
horizon. 
The first section with which he deals is that of Tyndrum and the 
Blackmount, in which, tracing the schists from the head of Loch Tay 
to Ciianlarich, he shows that they dip at low angles towards the north¬ 
west. After passing Crianlarich the dip is reversed, and he says that 
at this point there is probably a syncline. Proceeding farther up the 
Glen towards Tyndrum, the mica-schists and limestone are seen to 
dip towards the south-east. From this point, along the road leading to 
L-ingshouse and Glencoe, the schists are seen to roll over and pass 
upwards into the quartzites and gneiss of the Blackmount. He further 
says :—“ This section left no doubt on my mind that the gneiss form¬ 
ing the great central region of the Blackmount overlies the mica-slate 
T'yudrum and Loch Tay, and thus, as stated, is a newer formation. 
