214 



SERPENTINE, DIALLAGE, ETC. 



Gallery n * ca * disturbances which bent and contorted all the rocks of 



the country, and during which the cleavage was probably 



Wall- case 4. 



produced by mechanical pressure. 



Wall-case 5. 



Arranged and described by H. W. Bristow. 



L — Curling stone. Used in Scotland in playing the na- 

 tional game of curling, which is practised upon the ice 

 during the winter. 



The stone is made of the rock of Ailsa Craig in the Firth 

 of Clyde. Ailsa Craig consists of a single rock of greyish 

 compact felspar, with small grains of quartz and very mi- 

 nute particles of hornblende. — Presented by the Royal 

 Commissioners of the Great Exhibition of 1851. 



Serpentine, Diallage, &c. 



Serpentine is a silicate of magnesia combined with water, 

 with the addition of a minor proportion of oxide of iron. 



Some serpentines are said to be intrusive igneous rocks ; 

 others are decidedly metamorphic. The serpentine of the 

 Lizard district in Cornwall reposes on hornblende slates and 

 rock, and is said to have been erupted previously to the 

 granite of the same district, the former being traversed by 

 veins of the latter. 



(For details of the Serpentine and associated rocks of 

 Cornwall, see " Report on the Geology of Cornwall," De la 

 Beche, pp. 9 to 100, 473 to 499, and 500.)— H. W. Bristow. 



Serpentines are, however, often true metamorphic rocks, 

 good examples of which occur in Anglesea, where thin 

 streaks of Serpentine are truly interlaminated in the fo- 

 liated rocks, and even the larger masses possess a wavy 





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