IN GLEN TILT. 353 



to those among the sienite, but more nearly conforming in 

 their position to that of the stratified base of Ben y Gloe, do 

 not contain veins of sienite, or its gradations ; (parag. 40, 43, 

 50, 56, 70.) and this fact, while it goes to exclude the idea of 

 secretion, or any other tranquil process, attending the forma- 

 tion of the strata, as the source of the veins, argues that the 

 force, which disturbed the strata, was one which impelled the 

 fluid against, and among, them. 



129. Some of the main rocks of sienite were observed to lie 

 underneath lai'ge masses of strata, which are comparatively un- 

 disturbed, exhibit no veins of sienite, and are probably con- 

 nected with the great body to the south. This circumstance 

 favours the inference, that the direction of the impelled fluid 

 was either lateral, or from below. — That the direction of the 

 impulse was in some degree from below, may be inferred from 

 another circumstance. On the top of some of the rocks of 

 sienite, near the bridge, there are imbedded masses of horn- 

 blende-slate. Among these rocks, that referred to in the 

 plan by the figure 8 is one which exhibits such masses with 

 peculiar distinctness ; and, in its perpendicular face, the sienite 

 of the main rock is seen to the depth of several feet below 

 them. The sienite of this rock was found to have its specific 

 gravity 2.67 ; and of two masses of hornblende-slate resting 

 upon it, one has the specific gravity of 3.00, the other that of 

 3.01. Hence it appears, that the specific gravity of the horn- 

 blende-slate is to that of the sienite, as 100 to 89. Now the 

 specific gravity of the sienite, when fluid, whatever may have 

 been the cause of its fluidity, was probably less than it is at 

 present, and supposing it to have been somewhat greater, it 

 must have been considerably less than that of the hornblende- 

 slate : it can hardly therefore be imagined, that, if the fluid 

 sienite came from above among the fragments, it would have 



buoyed 



