112 Mr Lyell on a Dike of Serpentine cutting througJi 



Art. XXIV. — On a Dike of Serpentine, cutting through 

 Sandstone, in the County of Forfar. By Charles Lyell, 

 Esq. Secretary to the Geological Society of London, F. L. S. 

 Communicated by the Author. With a Plate. 



The natural history of serpentine is still involved in consi- 

 derable obscurity, and although of late years much attention 

 has been directed to its examination, there is, perhaps, no rock 

 of such extensive occurrence, and such decided characters, 

 whose geological relations are equally unascertained. 



In the locality which I am now about to describe, the con- 

 nections of the serpentine with the accompanying strata are 

 clear and unequivocal, and as it occurs there in great abun- 

 dance, and distinguished by its most striking mineralogical 

 characters, the phenomena which attend it can scarcely fail 

 to throw light on its general history. 



I was fortunate in having an opportunity, during the last 

 summer, of examining the spot where it is found, in company 

 with Professor Buckland, from whose active co-operation, 

 I derived great assistance. 



The age and relative position of the stratified rocks, with 

 which the serpentine is associated, are preliminary points, on 

 whose determination depends much of the novelty and im- 

 portance of the geological facts which it will be my object to 

 detail. 



The limits, however, of the present communication will not 

 permit me to enlarge on the history of these strata, which I 

 have carefully examined on the coast of Forfarshire, near the 

 Red Head, where the cliffs present us with a section of those 

 beds, which lie beneath the great conglomerate, and which form 

 the chief part of the Seedlay chain. The coast on the north of 

 Stonehaven, the rivers N. and S. Esk,Melgum,Islay,and others, 

 have also afforded me distinct sections, of the same formation, 

 which is there seen extending along the southern boundary of 

 the Grampians. From the study of these sections, I am en- 

 abled to state, with regard to the strata in question, that they 

 are younger than the greywacke and clay-slate, and older than 



