384 THE SOUTH SLOPE OF THE GRAMPIANS. 



Gareloch becomes less crystalline and more sandy, and disappears 

 beneath the clay slate near Eoseneath. The lower clay slates are 

 micaceous, deep blue or purple ; the upper are light blue or green and 

 silvery. This is the normal order of the beds on the south border of 

 the Western Grampians. 



Structure of Ben Lomond. Ben Lomond consists at the north 

 end of mica slate, often quartzose, greatly contorted, but with the dip 

 becoming more regular near Eowardennan on Loch Lomond. The 

 mica slate passes sometimes into grey talc slate when the beds become 

 intersected by a parallel vein of fine-grained syenite. Farther on, at 

 Sallachie, the clay slate rests conformably on the mica slate, and 

 according to Professor Nicol the bedding and cleavage coincide. 



Slate Rocks of the Trossachs. To the north of Callander the mica 

 slate and clay slate are well exposed in the Pass of Leny and on the 

 banks of Loch Lubnaig. In the Pass of Leny the lowest beds of 

 clay slate show distinct grains of quartz of sedimentary origin. Then 

 succeeds a great mass of chlorite slate full of reticulate quartz veins 

 associated with foliated rocks consisting of quartz and felspar, and 

 these rocks pass into blue talc slates, which are succeeded by mica 

 slates dipping to the north at an angle of 73 degrees. Ben Ledi 

 is a great mountain on the west of Loch Lubnaig, which consists 

 almost entirely of mica slate greatly contorted. Near Strathearn and 

 Comrie the clay slate is seen in contact with the syenite of Ben 

 Chonzie. The slates show distinct foliation. The syenite has the 

 hornblende more or less replaced by mica, and has the felspar abundant. 

 It sends veins into the slate without producing much alteration. But 

 as the slate rocks approach the syenite they become harder and more 

 crystalline. Then lenticular masses of red felspar and quartz become 

 mixed with the blue slate till the whole rock is converted into a fine- 

 grained gneiss. 



Mica Slate of Loch Earn. Mica slate predominates along the 

 north bank of Loch Earn, where it is greatly contorted, but with a 

 general dip to the north-east ; and Professor Nicol suggests that it here 

 forms an anticlinal axis, which probably continues the contorted beds 

 of Loch Long, Loch Lomond, and Loch Lubnaig. 



Central Gneiss and Quartzite. The gneiss of the Black Mount 

 and Breadalbane Highlands, according to Professor Nicol, forms a 

 synclinal trough and rests on both sides on mica slate. Near Killin 

 at the head of Loch Tay the mica slate is mixed with hornblende 

 slate and limestone. Eound Tyndrum, mica slate is intermixed with 

 beds of quartzite, with a varying dip to the south-east or north- 

 west. At Urchay Bridge gneiss rests on mica slate on both sides of 

 the valley. Beyond Urchay the gneiss continues by Inveroran and 

 King's House to the top of Glencoe. This idea of the gneiss being 

 the newer formation was opposed to the views of Murchison and 

 Geikie. High up the pass of Glen Shee towards Braemar are certain 

 limestones overlain by gneiss, which passes up into quartzite and forms 

 the higher parts of these mountains. Prom Ben Turk Bridge, where 

 there is a grey micaceous limestone dipping south-east, the valley 



