THK CAMBKIAN SKKJES IN N.>V. (WJiKNAliVONSHlJiK. 



;{:',!) 



(c) Section in the Road helov> the Cottages. 



The section below the cottages, under the stone wall (the " brick 

 wall " of Mr. Blake), seems to be no more favourable to his view 

 (fig. 4). He depicts two masses as included fragments of slate. 

 But the western mass is a greenstone dyke, about 8 to 12 inches 

 wide, close-grained and compact, especially at its lower part *. 



Fig. 4. — Section in Road near Br)jn Kfail. 



r 



y 







Vt 



~l:_ 



i:-'-hL'w 



1. Qiiartz-felsite 



2. Greenstone 





Porphyry of Mr. Blake. 



Baked slate of Mr. Blake. 



3. Wall of irregular stone blocks, 

 with a projecting ledge. 



The eastern mass could not be identified in every part, owing to 

 dirt, but a portion of it at any rate is an igneous rock of basic or 

 intermediate character. I was able to trace with rough approxi- 

 mation the junction-line of two different rocks, and fortunately 

 found two or three loose fragments, from which slides have been 

 prepared. These prove that the other rock at the junction is felsite 

 which has been cracked and veined with quartz and is entangled or 

 included in the greenstone f. There seems no doubt that the latter 

 is intrusive. Much of the rock just above the wall has been quarried 



* A slide prepared from this rock exhibits porphyritic crystals of two kinds 

 intergrown in a somewhat ophitic arrangement — felspars of earlier consoli- 

 dation, which are now replaced bj" a micaceous aggregate, and crystals, which 

 are ill-defined in mineral character, but may be altered felspars of later forma- 

 tion. The groundmass is minutely ci'ystalline, consisting of secondary products, 

 viridite, small flakes of chlorite, and what seems to be filmy mica, with many 

 needles and crystals of magnetite. It contains clear granules (probably quartz) 

 and some calcite, apparently belonging to minute amygdaloids. The rock is 

 probably an altered andesite. 



t This is apparently an andesite which has undergone subsequent alteration. 

 The porphyritic crystals in one slide show a mosaic, partly of filmy mica, with 

 a fringe of chlorite at the edge ; in another slide they are probably present, but 

 deformed by the crushing. In the ill-defined groundmass are dereloped brown 

 or greenish chloritic films, also very numerous granides and crystals of mag- 

 netite. 



