178 MR. E. B. BAILEY AND MR. M. MACGREGOE ON [June I912, 



(b) The persistence of a thin remnant of the Ballachulish Lime- 

 stone for many miles immediately above the Ballachulish Slide is 

 not what one would expect a priori. In fact, all the phenomena 

 revealed in the district here described can quite well be accounted 

 for, without invoking a slide at the base of the limestone at all. 

 The need for caution in interpreting the type sections in the 

 neighbourhood of Ballachulish, north and south of Loch Leven, and 

 in Glen Creran [1, pp. 605 & 609] is correspondingly increased ; 

 but the evidence in these localities is so definite that we have not 

 felt ourselves at liberty to abandon it. 



(c) In the great spread of southern schists, which we treat as 

 * unclassified ' for the purposes of the present paper, there are many 

 sheets of foliated basic igneous rocks. Some of these Dr. Peach 

 [6, chap, viij has clearly shown to represent ancient lavas, con- 

 temporaneous with the sedimentary schists among which they 

 occur. Many, on the other hand, have been proved to be intrusive, 

 but until recently it has been assumed that even these intrusions 

 are of earlier date than the folding of the schists. Since the recog- 

 nition of great horizontal movements in the schists, this interpre- 

 tation has been questioned. In the lower part of Glen Creran 

 (fig. 1, p. 165), for instance, many small, foliated, basic intrusions 

 of restricted distribution occur in equal abundance on the two sides 

 of the Ballachulish Slide, as if they are of later date than all, or 

 almost all, the movement which has taken place along the slide 

 [7, p. 188]. In like manner, in the district here described, sheets of 

 epidiorite occur fairly often for some distance below the base 

 of the ' unclassified schists,' and are especially common in this 

 position in association with the limestone of the Beinn Doirean 

 range. If a great slide is eventually demonstrated at the base of 

 the ' unclassified schists,' it will probably be necessary to assign 

 these epidiorite intrusions also to a late date in the tectonic history 

 of the district. 



y. Bibliography. 



1 . E. B. Bailey, ' Eecumbent Folds in the Schists of the Scottish Highlands ' 



Q. J. G-. S. vol. Ixvi (1910) pp. 586-618. 



2. H. Kynaston, in ' The Geology of the Country near Oban & Dalirially 



Mem. Geol. Surv. Scotl. 1908. 



3. 0. T. Olougii & E. B. Bailey, in ' Summary of Progress for 1907,' Mem. 



Geol. Surv. 1908. 



4. C. T. Clough, H. B. Maufe, & E. B. Bailey, ' The Cauldron-Subsidence of 



Glen Coe, and the Associated Igneous Phenomena ' Q. J. G. S. vol. Ixv 

 (1909) pp. 611-76. 



5. C. T. Clough, ' The Geology of Cowal ' Mem. Geol. Surv. Scotl. 1897. 



6. B. N. Peach, in 'The Geology of Knapdale, Jura, & North Kintyre' Mem. 



Geol. Surv. Scotl. 1911. 



7. E. B, Bailey, ' The Geology of the Neighbourhood of Fort William' Proc. 



Geol. Assoc, vol. xxii (1911) pp. 179-203. 



EXPLANATION OF PLATE X. 



Geological map of the neighbourhood of Glen Orchy, on the scale of 2 miles to 

 the inch, or 1 : 126,720. (By a draughtsman's error, the inch-scale has 

 been wi'ongly lettered on the map.) 



