126 Mi* Herschel on a Remarkable Occurrence of Serpentine 



regularly stratified, with a northerly dip, and contains sub- 

 ordinately greenstone slate. At a point on the sea-coast, 

 which is at a small distance to the east of Cadgwith, where 

 some quarries of a red and green serpentine have lately been 

 opened, and much of the rock exposed, a bed of shistose 

 greenstone is seen conformable to, and interstratified with the 

 serpentine, and in the midst of the greenstone is a granitic 

 rock, a few feet in thickness, which I term Sienite, merely be- 

 cause its position and decided geological connections forbid 

 me to apply to it the appellation of gneiss, or mica shist. It 

 consists principally of quartz, with a certain proportion of 

 mica disposed in laminae, so that specimens mav be selected 

 from it exactly resembling much of the mica shist of the 

 Grampians. A reddish felspar is occasionally present, and it 

 might then, in single specimens, be called gneiss. In its ge- 

 neral aspect it is not unlike much of the sienite of the Mal- 

 vern Hills, but it divides, upon being fractured, into slabs pa- 

 rallel to the strata in which it occurs. 



Mr Herschel has lately discovered at Predazzo, in the Ty- 

 rol, a locality well known to many geologists, a striking fact 

 with regard to the relations of serpentine with other rocks ; 

 for he has found layers of well characterized serpentine, form- 

 ing, as it were, the parting stratum between a granitiform 

 sienite, and a rock of dolomite. As there is so much analogy 

 between this fact and the case of the serpentine of Clunie, be- 

 fore alluded to, and the latter is so intimately connected, as I 

 have shown, with the subject of this memoir, I have requested 

 Mr Herschel to favour me with an extract from his notes, 

 explanatory of the specimens which he has brought from Pre- 

 dazzo. 



Akt. XXV. — Notice of a Remarkable Occurrence of Ser- 

 pentine at the Junction of Sienite with the Dolomite of the 

 Tyrol. By J.'F. W. Herschel, Esq. Sec. R. S. Lond. 

 and F.R.S. Edinburgh. Communicated by the Author. 



In the course of a Mineralogical i*amble through the Tyrol in 

 the months of August and September of last year, I encounter- 

 ed the phenomenon I am about to describe, in a small rounded 





