34 PEOF. T. G. BONKEY 02f THE HFRONIAN SEEIES 



The rocks forming the eastern zone of this " Huronian " region (the 

 donbtf-al belt west of Wahnepitae station) must be passed over rather 

 briefly ; not because they are deficient in interest, but because their 

 exceptional difficulty obliges me to speak of them with great hesitation. 

 Their distinction in the field from the typical Laurentian is obvious ;; 

 their special difficulty was not realized at the time, so that I only 

 took specimens from two localities. That from the first (eastern) 

 mass of rock referred to Huronian, the appearance of which in the 

 field has already been noticed, when examined under the microscope 

 is seen to consist chiefly of quartz, felspar, and a brownish mica. 

 The quartz occurs in rather elongated irregular grains, is fairly clear^ 

 but contains occasional fllms of mica : occasionalh^ there is a grain- 

 like spot of chalcedonic quartz. The felspar exhibits the striping of 

 plagioclase and the cross-hatched structure of microcline. The mica 

 occurs in small but fairly well-defined flakes, lightish brown, some- 

 times inclining to greenish, and (especially in the smaller separate 

 flakes) almost colourless *. The rock certainly exhibits a fragmental 

 structure with secondary reconstruction. Is it, then, a rather fine- 

 grained gneiss, modified by pressure, or an arkose of similar materials 

 in which rather marked reconsolidation has occurred ? Pressure- 

 indubitably has acted, as may be seen by the occasional cracking of 

 the felspar and the strain-shadows which sweep across the quartz 

 grains. I incline, though not without hesitation, to the former view, 

 and to consider that, as in Scotland, an important fault has brought 

 up some of the more fine-grained rock of the Laurentian series, and 

 in so doing has given it a pseudoclastic aspect. 



The constituents of the specimen from the western side of the 

 belt are very similar to the above. In the field I took it for a 

 variety of a fine-grained quartzite, but, though imder the microscope 

 there is indubitably a structui-e suggestive of a clastic origin, I 

 am doubtful whether this is not really a member of the Archaean 

 series modified by subsequent pressure. There has certainly been 

 mineral change in either case, and until more evidence is obtained 

 I think it safer to state the alternatives. It contains some smaU 

 crystals, generally aggregated, of a dark olive-brown, almost opaque 

 mineral, probably a very ferruginous mica or chlorite. 



After this we enter a region where our hesitation is at an end, 

 and microscopic examination confirms the impression formed in the 

 field that (excepting some unimportant intrusions of a basic igneous 

 rock) we are dealing with a series of clastic origin. I have already 

 described the general succession in this region f. Time will be saved 

 if in noticing their microscopic structure, I group them lithologically 

 as follows : — 



(A) Ordinary quartzites. Quartzites containing conspicuous 



fragments. Pine-grained schistose quartzites. 



(B) Agglomeratic or conglomeratic rocks. 



* It contains some crystalline grains, often aggregated, of a mineral granular 

 in texture, varying from a golden-brown colour to all but opaque, perhaps an 

 impure sphene or rutile. 



T See also Logan, p. 52, for one more detafled in a neighboxiring district. 



