part 4] THE SCHISTS OF the schichallion distkict. 423 



16- The Geology of the Schists of the Schichallion Dis- 

 trict (Perthshire). By Ernest Masson Anderson, 

 M.A., B.Sc, F.R.S.E., F.G.S. (Bead March 14th, 1923.) 



[Plate XXV— Map & Section.] 



Contents. 



Page 



I. Introductory 423 



II. Divisions of the Quartzite Group 425 



III. The Beds between the Quartzite and the Struan Flags 427 



IV. Chronological Order of Succession 429 



V. Structure of the Schichallion Area 433 



VI. Line of Contact between the Dalradian Series and the 



Struan Flags 435 



VII. Regional Metamorphism 438 



VIII. Summary and Conclusions 441 



I. Introductory. 



The district studied extends from the northern slopes of Cam 

 Mairg across Strath Tumrael, and includes a part of the valley of 

 the Errochty Water. Except for some later intrusions, it is occu- 

 pied entirely by crystalline schists. These belong in part to the 

 series of Struan Flags — the probable equivalents of the Moine 

 Gneisses of the more northern Highlands — and in a greater part 

 to the so-called Dalradian Series, which here projects along a 

 north-and-south axis for about 7 miles into the flags. The area 

 includes the best development of the well-known Schichallion 

 Boulder Bed, and has a historical interest from its association Avith 

 Maskelyne's Schichallion experiment, which in itself led, at. an 

 early date, to a certain study of the geology. 1 



The district was mapped about the year 1900 by the late 

 Mr. J. S. Grant Wilson, of the Geological Survey. Although a 

 succession not previously recognized forms the basis of the map 

 now presented, the latter follows Wilson's in many of its main 

 features, and the investigation of the area would have been a task 

 of far greater difficult} 1- without the guidance of his previous work. 



I am to a great extent indebted to Mr. E. B. Bailey for the 

 inspiration which led me to take an interest in the problems of 

 the Southern Highlands. Mi-. Bailey, in a previous traverse of the 

 ground here described, had anticipated that part of the conclusions 

 of this paper which concerns the divisions of the Quartzite Group, 

 and the relations of the rocks on its opposite sides. He has also 

 made as yet unpublished observations on this Group in the neigh- 

 bouring district of Blair Atholl, which he kindly gives me leave to 



' John Playfair, ' Account of a Lithological Survey of Schehallien, made 

 in order to Determine the Specific Gravity of the Rocks which Compose that 

 Mountain ' Phil. Trans. Roy. Soc. vol. ci (1811) p. 347. 



Q. J. G. S. No. 310. 2 g 



