§22. 



MICA-SCHIST AND GNEISS. 



845 



22. Mica-schist and Gneiss. — These rocks are widely 

 spread over and around the masses of unstratified plutonic 

 rocks. They occur in Caernarvon and Cumberland, but 

 are of inconsiderable extent in England. In Scotland they 

 extend over great part of the Highlands, and largely prevail 

 in the Hebrides; they form the mountain-ranges of the north 

 of Ireland, and cover large areas in Londonderry and 

 Donegal. 



The most striking features of these rocks, are the flexures 

 and contortions in which they are so generally folded ; 

 proving the soft and ductile state in which the component 

 materials must have existed, for they present every variety 

 of sinuosity and curvature imaginable. 



The Isle of Lewis (one of the Hebrides) so admirably 



Lign. 1S9 —Curved Gneiss in the Isle of Letvis. 

 (Br. Macculloch's Western Isles.) 



illustrated by Dr. Macculloch, is remarkable for the contor- 

 tions observable in its precipitous cliffs of gneiss, and the 



