HornUende Laiiiprophyrc Dyke at Richmond, P. Q. 319 



ties of the elongated patches in which it often occurs. 

 ■The roclv is no longer fresh. The feldspar, of which a 

 very considerable portion is plagioclase, is a good deal 

 decomposed, and the hornblende is altered in a very pecu- 

 liar and hitherto unobserved manner. ..." 



It is a very frequent associate of the serpentines 

 throughout the Eastern Townships, and is commonly 

 believed by miners to be a necessary condition of the 

 occurrence of the better class of asbestos deposits. It is 

 enclosed in the serpentine, and from this fact, as well as 

 its finer crystallization near the contact, is presumably 

 intrusive through it, although the actual contact is gener- 

 ally concealed. 



The porphyrite consists of a fine feldspathic base, 

 containing phenocrysts of plagioclase and a few large 

 individuals of epidote and chlorite, possibly representing 

 primary hornblende. It, too, is considerably decomposed, 

 and it contains veins and secondary aggregates of quartz, 

 chlorite and epidote. No quartz, that is certainly primary, 

 could be distinguished. The relations of this rock are not 

 so easily determined as' the last, yet are tolerably certain- 

 It appears to have reached about the same degree of 

 decomposition as the granite, but has suffered less dynamic 

 metamorphism, and although the difference in the suscep- 

 tibility of various rocks to metamorphic agencies prevents 

 this fact from furnishing a safe clue to their relative ages, 

 yet it cannot be entirely overlooked. The porphyrite 

 also contains fragments of Cambrian slate which probably 

 elsewhere overlies the serpentine, but this fact, again, is 

 not yet clearly established. But a block, apparently of 

 the same agglomerate which is found in Lot 13, Eange 

 XIII. of the township of Cleveland, nearly two miles 

 north of the serpentine belt, contains fragments which are- 

 macroscopically indistinguishable from the hornblende 

 granite just described. This evidence, which appears con- 

 clusive, is substantiated by the fact that the course of 

 23 



