420 ME. J. TAKKINSON ON THE GEOLOGY OF [Aug. I903, 



but not rarely in well-built crystals which have formed in many 

 instances across the foliation. These, no doubt, are the alteration- 

 products of the primary ferromagnesian constituent, and are locally 

 associated with clouds of magnetite-granules. Among these mica- 

 flakes, and also in the originally more felspathic part of the rock, 

 are long crystals of colourless epidote, connected with a considerable 

 quantity of carbonate and a mosaic of translucent grains, partly 

 representing the original felspar. 



In such a rock a considerable transference of material must have 

 taken place ; in that from Bossiney Haven the complete recon- 

 struction has been accomplished, and I conclude that we have to 

 deal with basic rocks of the composition of a diabase or diabase-tuff 

 in which the lime of the felspar, together with part of its alumina, 

 has gone towards the making of the epidote, while the remainder of 

 the alumina, together with that which the augite may have contained 

 plus its magnesia and iron, have aided in producing the biotite. 

 Eutile, magnetite, and sphene arose from the reconstitution of the 

 ilmenite. 



Study of several slides suggests the following sequence of events 

 as comprising the history of these rocks : — 



Eeconstruction — aided perhaps by contact — produced first epidote 

 and then green biotite, and was followed by pressure. The epidote 

 and the quartz were saved by the yielding of the carbonates, chlorite, 

 and biotite (a result dependent on the proportion of hard to soft 

 minerals). On the cessation of the pressure the calcite was recon- 

 structed ; but since there is evident corrosion of the epidote and 

 biotite by both calcite and quartz, I infer an introduction of addi- 

 tional mineral matter in solution (carbonate of lime and silica) j 

 which also produced the intimate association of the quartz and 

 carbonates above recorded, and which was attended possibly by a 

 revival of crystallization iu other minerals than calcite. 



The late introduction of extraneous material is supported by the 

 following evidence. Among the rocks of Trambley Cove, which 

 appear to be a slaty variety of the Volcanic Series, occur irregular 

 rope-like bands, occasionally mere knots or eyes, consisting almost 

 entirely of tourmaline. A thin section, cut transversely to the 

 direction of the band, is composed of prisms of tourmaline lying 

 in two planes at right angles, and packed closely together to the 

 almost entire exclusion of interstitial material, which, when found, 

 is quartz. The dichroism of the tourmaline is 



E, pale pinkish-brown. 

 O, bluish-green, 



The absorption is considerable. 



The crystalline arrangement shows strong flexures, but the 

 prisms are unbroken, and I am indebted to Prof. Bonney, to whom 

 I showed the slide, for the suggestion that tourmalinization took 

 place after the pressure, the prisms forming along the flexures so- 

 produced. 



