NOTES ON INTRUSIVE ROCKS NEAR ST. JOHN, N. B. 63 



augites, and lath-shtped feldspars with flow structure. The 

 augites of the groundraass are sharply outlined, not decomposed, 

 and very pretty. 



6. ? 1 Tachylite (basic glass). Locality same as the last, from a 

 small branch dykelet. 



Very fine grained, with a few small crystals in a decomposed 

 base, traversed with numerous cracks doubtfully perlitic, hence 

 perhaps a devitrified glass. 



Nos. 2-6 are none of them the usual style of the Huronian 

 diabases, although ISTo. 3 is technically a diabase ; a more complete 

 knowledge of the dyke would, perhaps, show it to be normally 

 an augite-porphyrite. I am inclined to think that the usual type 

 of the post-Cambrian dykes will be found to be augite porphyrite 

 and basalt, that of the pre-Cambrian ones either diabase, connected 

 with the '* Huronian " rocks, ov diorite por2)hi/rite, connected with 

 the intrusive granite-diorites. No. 2 may be a later dyke than 

 3-6 ; it had somewhat that appearance in the field, and is fresher 

 in section. 

 N'o. 78-187. Dolerite. Devil's Back. 



Coarse-grained, with crowded porphyritic crystals of augite in 

 a groundmass of small augites and feldspars. 



The large augites are very much zonally cracked — no variation 

 in composition in the different layers, so that I take it to be the 

 result of sudden cooling in a rock half solidified. The cooling 

 was accompanied and followed by some motion of the mass, which 

 caused the crystals to break up more or less. 



This tallies with note on the Cambrian dykes as to composi- 

 tion. Though the evidence on the composition of the post-Cam- 

 brian dykes is exceedingly meagre as yet, yet it points uniformly 

 in the one direction — that of a community of origin. 

 69-76. Apliie (fine grained granite). ^"Ox-ljow Reef," first 

 rock next granite. 



A granular mixture of orthoclase, quartz and secondaiy 

 epidote. Occasional zircons, a little magnetite. Orthoclase 

 tends to be idiomorphic. No plagioclase observed. 



