528 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 6, 



spheroidal brecciiforin rock similar to some of those described above. 

 These shales are often much twisted and broken, and are interstra- 

 tified here and there with interrupted bands of altered wacke, which 

 are also brecciated. There are many points of interest connected 

 with the brecciiform stones at this place; but these cannot be 

 considered here. The most notable feature about the beds is the^ 

 occurrence of limestone in the shales. Among- much disturbed and 

 brecciiform beds may be seen a large block of limestone, four feet 

 across. It looks as if it had been forcibly pushed into its present 

 position; for the shales are all puckered and squeezed about it. 

 Many smaller calcareous fragments occur in its vicinity. In their 

 neighbourhood the beds are abundantly veined with carbonate of 

 lime; but these veins are chiefly confined to an iiTegular band 

 or area along the direction of the strike. There can be no doubt 

 that the veins have resulted from the dissipating, in situ, of a lime- 

 stone, they and the honeycombed and amorphous-shaped blocks 

 being all that now remain of that bed. A yard or two from 

 this point may be seen irregular nodular calcareous bands in 

 dark greenish shales, which are here much less disturbed. The 

 confusion observable in the former case must therefore in 

 great measure be due to the withdrawal of the limestone. 

 Leaving these shales and continuing the section southward we come 

 at once upon highly metamorphic strata, consisting chiefly of ser- 

 pentine with interbedded dioritic masses and occasional areas of 

 felspar-porphyry. The bed immediately associated with the dark 

 greenish shale is a serpentine ; but the junction, unfortunately, is not 

 well seen. There can be no doubt, however, that the schistose ser- 

 pentine is merely a metamorphosed shale. All serpentine-rock 

 contains less or more alumina, and many of the ophiolites of this 

 neighbourhood are in this way very impure ; indeed it is often 

 impossible to distinguish between highly magnesian shale and 

 impure schistose serpentine. Geologically, the latter is only an 

 altered condition of the former. The veins of diallage which are 

 sometimes found in these shaly and schistose varieties may not 

 improbably represent calcareous veins similar to those that traverse 

 the dark shales alluded to above, subsequent metamorphic action 

 having converted them into diallage. The silica and magnesia 

 necessary to this change would, of course, be derived from the 

 impure magnesian rocks through which the veins ramify, and which 

 at the time the veins were forming were assuming their present ophio- 

 litic character. In like manner, the bronzite, especially in the more 

 compact serpentines, may partially represent the carbonate of lime that 

 was diffused through the rock before alteration began. Crystals of 

 bronzite and diallage are so abundant throughout large areas of 

 serpentine as frequently to form a JiftJi, and- sometimes even a 

 third) of the bulk of that rock. The condition of the beds before 

 metamorphism ensued may therefore have been that of impure or 

 muddy dolomitic or magnesian limestones. In support of this view 

 it may be mentioned that, in less altered areas of the district, 

 limestone has been met with which was sometimes mae-nesian. 



