part 4] THE SCHISTS OF THE SCHICHALLTOJf DISTEICT. 433 



V. Structure op the Schichallion Area. 



The northern syncline. — At their northern limit the 

 Dalradian rocks are enclosed in a little syncline, which pitches out 

 northwards, and are underlain, hoth in that direction, and on 

 the east and west, with only a gentle discordance, by the Struan 

 Flags. Within the syncline is an ascending sequence, from the 

 Grey Schist to the Schiehallion Quartzite. 



Followed southwards the syncline broadens, and an area of 

 Killiekrankie Schist appears in its centre. At. the same time, the 

 eastern limb becomes reversed. Somewhat south of the Errochty 

 a structure occurs, which may be described by saying that the 

 axial plane of the syncline is shifted a mile and a half to the west. 

 The strike of the eastern limb is altered from north and south to 

 east and west, resuming its original direction about 2 miles north- 

 east of the summit of Beinn a' Chuallaich. The reversed dip of 

 this limb is meanwhile maintained at rather a low angle. 



The western limb becomes unrecognizable a little beyond the 

 point where it crosses the Errochty, and the further use of the 

 term ' syncline ' refers only to the fact that Dalradian strata are 

 bordered on both sides, and probably underlain, by flags. South- 

 wards the syncline, as so defined, becomes split by a subsidiary 

 anticline. The first sign of this is the appearance of a mass of 

 Schiehallion Quartzite, which forms the summit of Ben a' Chual- 

 laich, and is bordered on both sides by Killiekrankie Schist. 

 A strip of Boulder Bed then appears within the Quartzite, which 

 at one point is seen in contact at both sides with, and overlying, 

 a vertical upfold of ' honeycomb rock.' A little farther south, 

 both the White Limestone and the Banded Series become visible. 

 Although there is no sign of ordinary faulting, the eastern 

 margin of the anticline is here a line of movement, as the 

 White Limestone is brought sharply against Killiekrankie Schist, 

 and nearer the Tummel the Banded Series is in contact with 

 Schiehallion Quartzite. 



South of the Tummel the ' crest ' of the anticline is formed by 

 Grey Limestone and Gre} r Schist. On approaching Schiehallion 

 the strike bends round through south-east to east, while the dip of 

 both limbs of the anticline, and of the eastern limb of the main 

 syncline changes from steeply east to an angle of about 55° 

 southwards. 



The structural succession. — In the foregoing para- 

 graphs it has been assumed that the structural succession seen at 

 the northern end of the Dalradian projection is the general order 

 of superposition in the district, despite minor folds, or even over- 

 folds. This assumption is in agreement with the relations of 

 Quartzite and ' honeycomb rock ' south of Ben a' Chuallaich. It is 

 strengthened by the behaviour of the two main groups in the area 

 north-east of Schiehallion. Here a quartzite, which probably 

 belongs to the Struan Flag Series, and, if not, certainly overlies 



