190 PROCEEDINGS OF TIIE GEOLOGICAL SOCIETY. 



east of the last section. Comrie, though remarkable both for its 

 picturesque beauty and for the frequency of the earthquake-shocks 

 felt there, has met with less attention from geologists than the in- 

 teresting nature of the phenomena around it might demand ; and I 

 am not acquainted with any detailed description of its formations. 

 The village lies in the bottom of a wide, flat valley, shut in on all 

 sides by hills, and traversed by the Earn, Ruchill, and Lednock rivers, 

 which unite at this place. On the north and west the primary 

 mountains rise high and rugged, whilst the trap and Old lied Sand- 

 stone form a lower range, separating it from the central plain. Upper 

 Strath Earn is evidently a great valley of denudation, with rounded 

 knobs of slate and trap, smoothed and striated by glacier- action, rising 

 through the level sheet of detritus. 



The section, fig. 6, represents the rocks as seen on nearly a north 



N. 



Fig. 6. — Section at Comrie. 



Ben Chonzie. Lednock. Comrie. 



Syenite. a a a Alluvium. b Red Sandstone. 



Clay-slate. 



a. Trap-dykes. b. Greenstone. 



and south line passing from the granite, or rather syenite, of Ben 

 Chonzie, through Comrie, to the red sandstone of the central valley. 

 Where it begins in the south, the strata are chiefly fine-grained red 

 sandstones intermixed with grey micaceous beds or dark-red sandy 

 shales covered with bright-green blotches. In the low ground the beds 

 lie at a low angle, but towards the north dip at 70° to S. 15° E., and 

 rest on thick masses of coarse conglomerate. In this rock the strata 

 are nearly vertical, with a direction from E. 28° N. to W. 28° S. It 

 appears to have been elevated by the greenstone on the north, which 

 runs in a series of low, rounded, and interrupted knolls from N.E. to 

 S.W., separating the Red Sandstone from the primary formations. 

 The changes that the igneous rock has effected on the conglomerate 

 are very remarkable. In one place, large, distinctly rounded boulders 

 are imbedded in a basis of porphyritic or amygdaloidal trap, inter- 

 sected by veins of chalcedony and calc-spar. It looks almost as if, 

 in some period of violent convulsion, a bed of molten lava had forced 

 itself in amidst a heap of water- worn shingle, and kneaded up the 

 loose boulders into its own mass. Probably, however, it is only a 

 true conglomerate with a basis of broken-down or decomposed trap, 

 which has subsequently been semi-fused, thus giving the mass the 

 aspect of an igneous rock. 



The boulders in the conglomerate range in size from fine sand or 

 gravel to masses of nearly a foot in diameter. Lying close to the 

 foot of lofty mountains of the primary formations, it might naturally 

 be expected that the conglomerate should be composed of fragments 



