122 Mr Lyell on a Dike of Serpentine cutting through 



strata of sandstone are cut off' at an angle, and are evidently 

 disturbed, the dike of serpentine itself, pursues its course un- 

 interruptedly, and in a direct line for many miles, both to the 

 eastward and westward. 



If we attempt to follow the course of this dike, we find 

 that the country is deeply buried under gravel, which consists 

 chiefly of pebbles of primitive rocks, washed down from the 

 Grampians, and that the subjacent strata are only visible at 

 those points where, as at the West Balloch, the strata are in- 

 tersected by deep ravines, or " dens, 1 ' as they are called, 

 through which rivers descend, and which they appear, in a 

 great measure, to have worn for themselves. 



The first of these, towards the east, is at the distance of 

 about two miles, at Proson Haugh, on the Proson, a mile be- 

 low Pearsie, the seat of Charles Wedderburn, Esq. The blue 

 serpentine there resembles the great dike on the Carity, and 

 contains diallage. Its junction with the regular strata is not 

 seen, as it has decomposed much ; but an altered rock, ap- 

 proaching in its characters to jasper, and traversed by numer- 

 ous veins of brown spar, crosses the river a short distance 

 above it. 



Rather more than a mile west from thence, in the same line, 

 the serpentine reappears on the south-east, at the bridge of 

 Cortachie. The red slaty sandstone, there seen on its north- 

 ern side, has a northerly dip, which is a rare occurrence in the 

 strata at the foot of the Grampians, in this district in Scotland. 



I have not yet traced the serpentine farther to the north- 

 west, but have sought for it in vain on the North Esk, about 

 fifteen miles in a direct line from the last mentioned locality, 

 although the section of the rocks on that river, which have 

 been so well described by Colonel Imrie,* is complete. There 

 are, however, on the North Esk dikes of gi'eenstone, which 

 cross the river in the same direction, and nearly in the same 

 place as the serpentine might be expected to occupy. 



It will now be interesting to return to the Carity, and to 

 trace the serpentine stretching in an opposite direction towards 

 the W. S. W. After leaving the W. Balloch, it first reap- 

 pears at the distance of about four miles in the farm of Burn- 



* Trans. Royal Society, Edinburgh, vol. vi. — 3. 



