634 REPORT— 1901. 



as given above appears to be an ascending one, proceeding from the margin 

 inwards, the ■well'marked zone known as the Loch Tay Limestone forming a sort 

 of datum line, from which one can recognise the positions of the lower and upper 

 scliists. 



3. It is supposed that the movements which plicated the rocks of the Highlands 

 were directed from the centre outwards, or from the N.W. towards the S.E. This 

 is shown by the fact that where the bedding can be traced the overfolding is 

 generally towards the S.E. Also the foliation, where it has been folded, faces in 

 the same direction. 



4. In the eastern part of the region we suppose that the bedding has been 

 folded into a series of isoclines facing the south-east, and that a foliation has been 

 developed roughly parallel to the axes of the folds in the bedding, thus making 

 the foliation appear to be roughly coincident with the original planes of stratifica- 

 tion. At Comrie, in Perthshire, the axes of the isoclines in the bedding are nearly 

 vertical, but with a slight hade towards the N. W. The axes of the isoclines get 

 gradually lower and lower as we proceed towards Loch Tay. In the same way 

 the foliation planes are nearly vertical along the frontier, but get flatter and flatter 

 as we proceed northwards. 



.'5. In tracing these rocks towards the south-west an increasing crumpling and 

 folding of the foliation planes, accompanied by more intense metamorphism, is seen 

 to take place : this is made evident in approaching the shores of Loch Katrine and 

 Loch Lomond, but it seems to have reached its maximum in Cowal. 



?>. In Oowal, along the Firth of Clyde, the position of the foliation planes has 

 been reversed, now dipping towards the south-east. Between the Firth of Clyde 

 and Loch Fyne the foliation planes have been much crumpled, and still later 

 divisional planes have been developed in them, this being a region of the most 

 intense metamorphism. 



4. The Granite of TuVoch Burn, Ayrshire. 

 ^y Professor James Geikik, F.K.S., and John 8. Flett, 31. A., D.Sc. 



The granite of Tulloch Burn, Ayrshire, is a small mass occupying an area of 

 three or four square miles on the headwaters of the Irvine and the Avon. Much 

 of the outcrop is covered with drift and peat, but good exposures of the granite and 

 the contact altered rocks can be obtained in the Tulloch Burn, a tributary of the 

 Irvine and on the Avon. The prevalent type is a flesh-coloured biotite-granite, 

 which often contains hornblende and sometimes decomposed augite. This passes 

 at its margins into rocks of intermediate or basic composition, which include 

 various types of diorite, hyperite, and gabbro. The evidence points to the origin 

 of these rocks by a process of differentiation, and both in this respect and in the 

 rock species which have been developed the resemblance to the granites of the 

 Southern Uplands is very close. The material microscopieallv examined 

 includes:— Graphic Granite and Granophyric Granite (in segregation veins); 

 Biotite Granite, Biotite Hornblende Granite, Biotite Augite Granite; Tonalite 

 (intermediate between Hornblende Biotite Granite and Diorite) ; Quartz Horn- 

 blende Diorite, Quartz Augite Biotite Diorite, Quartz Hypersthene Diorite ; 

 Biotite Augite Diorite, Hornblende Diorite, Hypersthene Diorite ; Hyperite and 

 Gabbro. 



This mass is intrusive into the Lower Old Red Sandstone, which at Lanfine, a 

 little west of this, has yielded Cephalaspis Lyelli. The Old Red Sandstone is 

 indurated and often hornfelsed to a varying distance from the margin. The new 

 minerals developed are Augite, Hornblende, Biotite, Magnetite, Tourmaline, 

 Spinel, and possibly Sillimanite : Calcite, Chlorite, and Epidote are often present, 

 but appear to be secondary after some of those mentioned. 



Many dylies penetrate the sandstones, and most of these are undoubtedly 

 apophyses of the Granite. They are mostly Diorite Porphyrites or Quartz Diorite 

 lorpbyrites, wlilch may contain Biotite, Augite, Hornblende, or Hypersthene. 

 Syenite Porphyries also occur, and occasionally small veins of more acid character, 



