ISO Mr Lyell on to Dike of Serpentine cutting through, 



dike of greenstone at Clunie, in Perthshire, at whose contact 

 with a bed of limestone, a thin band of serpentine occurs. 

 The author has observed, " that the greenstone, as it ap- 

 proaches the limestone, acquires a finer texture and a laminar 

 structure. The lamina? are often intersected by cross fissures, 

 dividing the whole into cuboidal masses, which sometimes de- 

 compose still further into spheroidal forms. A regular gra- 

 dation may be traced from the greenstone to the serpentine, 

 in proportion to its approximation to the limestone. 1 ' 



I have visited Clunie, and was much struck with the exact 

 resemblance of the fine-grained rock above mentioned, and 

 that which appears at the edge of the serpentine dike at the 

 West Balloch. I find, however, that all the specimens which 

 I possess of the fine-grained greenstone of Clunie effervesce 

 with acids, which the rock at the Balloch does not. These 

 two cases may be regarded as the converse the one of the 

 other, for the greenstone on the Carity is as insignificant in. 

 quantity, when compared to the dike of serpentine, as is the 

 vein of serpentine at Clunie when compared to the accom- 

 panying greenstone dike. It is much to be regretted, that on 

 the Carity, the rock in contact with the fine-grained green- 

 stone on the side opposite to the serpentine dike, is not seen. 

 I caused a deep trench to be sunk, but did not succeed \n 

 reaching any rock, though the soil strongly indicated a de- 

 composed serpentine. I think it highly prohable, that the 

 variety of serpentine, which has here disappeared, is that 

 which I have already described, into whose composition the 

 magnesian carbonate enters so largely ; for a mass of this 

 rock is the first which appears in situ, on this side of the ri- 

 ver, approaching much nearer to the great dike than any of 

 the dolomitic serpentine on the opposite bank, as the section 

 will explain. 



I have before stated, that, in another place, on the right 

 bank, in an interval left by the decomposition of the dolomi- 

 tic variety of serpentine, blocks of greenstone indicate clearly 

 the association of that rock with the serpentine. The spot 

 where this occurs, is distant about fifty yards from the thin bed 

 of fine grained greenstone to which T have alluded, and it is a 

 circumstance which confirms my supposition, that the dolomi- 



