42 ROCK-METAMORPHISM. 



carbacid rock having become serpentinized, unless it be the 

 " oficalces " that hang on to the dykes of euphotide, and the 

 adjoining disrupted beds of alberese limestone, in different places 

 between Genoa and Spezzia. 



In this connexion it may be remarked that such instances may 

 be taken to support the view, held by J. Dana, that the West- 

 chester hemithrenes were originally limestones, and have since 

 been impregnated with silicic acid. 



Another idea as to the origin of ophitic rocks was broached 

 by the late Prof. R. Harkness. It is thus expressed : " The 

 serpentinous limestones of Connemara are of local occurrence ; 

 they usually appear in such districts as exhibit the strata highly 

 contorted and broken up. The lines of lamination in the lime- 

 stone strata have been opened, and the laminae have been frac- 

 tured across, in consequence of the contortions to which the 

 strata have been subjected ; and into these openings and frac- 

 tures the serpentine has been subsequently introduced. ... In 

 the calcareous band which lies east of Lisoughter, and which 

 extends to near Oughterard, the laminae have not been opened 

 and broken by contortions; and from it the serpentine is 

 absent" *. This hypothesis, which appears to us to be more 

 ingenious than sound, we consider is based on insufficient data 

 obtainable in the field and the cabinet. 



* Quart. Journ. Geol. Soc. vol. xxii. pp. 509 & 511. 



