IN GLEN TILT. 305 



3. In the immediate neighbourhood of Blair, the river 

 Tilt, and the small stream of the Brinavie, which runs through 

 the Duke of Atholl's pleasure-grounds, afford, each of them, a 

 deep section of the rock, and shew that it is almost wholly 

 formed of strata. The slight examination which we gave to 

 these, led us to conclude, that they consist, for the most part, 

 of granular quartz, mica-slate, hornblende-slate, and granular- 

 limestone. An observation made with an instrument for the 

 purpose *, upon the strata by the side of the Tilt, not far above 

 its junction with the Garry, determined the stretch to be about 

 N. 60° E. ; and another upon the strata in the bed of the Ba- 

 navie gave N. 58° E. This near coincidence must, however, 

 be regarded as accidental ; for the position of these strata is 

 varied by many inflexions of their planes, especially on the 

 banks of the Tilt. The dip is every where southerly, at an* 

 angle which varies considerably, but is commonly small for, 



primary 



will be remembered, I hope, that the occasion called for a statement of the whole 

 ease ; and, besides, while the mere outlines of theory are still under discussion, it. 

 seems expedient, in describing phenomena which strongly affect any single point 

 of importance, to enter largely into the concomitant circumstances -, since it is im- 

 possible to foresee what may, or may not, become subservient to a more precise' 

 determination of the truth. 



* This instrument was a Clinometer, in its earliest form, without the brass 

 plate. Though it was by no means so accurate as the improved one, the obser- 

 vations may, in general, be considered as within a few degrees of the truth. 

 Some error may occasionally have arisen, from the surface of the rock being ra- 

 ther uneven, or from its not being quite parallel to the plane of stratification., 

 For a more convenient comparison of the various positions of the strata, the 

 bearing of the line of stretch is* throughout, indicated by the number of degrees 

 east of north. As the line of dip is always at right angles to that of the stretch, 

 it was thought sufficient to mark on which side the depression lay, by mention- 

 ing that of the four, or of the eight, principal points of the compass, which was. 

 nearest to its bearing. 



