642 



MESSES. CLOTTGH, MAT/EE, AND BAILEY ON [Xov. 1909, 



An example of granitic intrusion belonging actually to the dyke 

 period is afforded by a band of aplitic composition, which has been 



traced between Meall 

 Pig. 3. — Porphyrite dyke traversing rliyolites 

 at the foot of the northern front of the 

 Buachaille Etive Beag (about -^ nat. 

 size). 



PORPHYRITE 



DYKE 



[The figure shows that the walls of the country-rock 

 are counterparts, the one of the other.] 



Odhar and Stob Ban 

 on the south side 

 of Glen Etive. It 

 cuts some of the 

 north -north-easterly 

 porphyrite dykes, 

 although it is inter- 

 sected by others. 

 The boundaries of 

 this intrusion have 

 been inserted on the 

 general map (PI. 

 XXXIV). 



In our district, 

 therefore, the main 

 dyke - phase inter- 

 venes between the 

 uprise of the Crua- 

 chan and Starav 

 Granites, and is in 

 part contempora - 

 neous with the in- 

 trusion of the much 

 smaller mass of 

 Meall Odhar. Taking 

 a more general view, 

 we find similar dykes 

 widely distributed 

 both in the High- 

 lands and in the 

 Southern Uplands. 

 The latest stratified 

 formation which they 

 ever traverse is the 

 and in other districts 



Lower Old Eed Sandstone, as in Glen Coe 



they have yielded a profusion of pebbles to the Upper Old Peed 



Sandstone conglomerates. 



One of the dykes in Allt nan Gaoirean and several in the clean-washed 

 section of Glen Dochard are intensely sheared in a direction which may make 

 any angle up to 45° measured from the alignment of the dyke. The structure, 

 like that which affects the early fault-intrusion of Allt Coire an Easain, has 

 deformed the phenocrysts, especially the ferromagnesian minerals, which are 

 drawn out into long lenticles. It is generally traceable right up to the dyke- 

 margin, but is only doubtfully recognizable in the massive Cruachan Granite 

 outside. After the shearing movements ceased, a certain amount of reerystal- 

 lization has taken place, which may be due to contact-action by the Starav 

 Granite, but the shearing itself may well be due to movements attending the 

 introduction of the latter mass. — October 22nd, 1909.] 



