GRANITIZATION OF ACIDIC LOWER HURONIAN SCHISTS 237 



pebbles are of granite, quartz-porphyry, felspar-porphyry, felsite, of 

 various cherty rocks derived from the iron formations of the Lower 

 Huronian and of schists and phylhtes. Of these perhaps those which 

 stand out most prominently, and which are of most general occur- 

 rence, are of the granite rocks, and more especially of a light- colored 

 grayish or pinkish and somewhat porphyritic granite. Sometimes 

 pebbles are almost or entirely wanting, and then the conglomerate 

 passes into the Dore slate — a somewhat rare phase of the Dore For- 

 mation, but occurring at several points, notably at the mouth of the 

 Dog River. The Dore agglomerate is also rare, but occurs promi- 

 nently at several points in the northern part of Michipicoten. It is 

 a somewhat fine-grained chloritic or sericitic rock, containing some- 

 times a great many, but generally a very few, fragments of rocks, 

 usually of the same chemical composition as the ground-mass, but 

 more coarse-grained, and very frequently porphyritic. It is occa- 

 sionally with difficulty distinguishable from the water-formed rock. 

 When without fragments it becomes the Dore tuff — a form in general 

 of very unusual occurrence. 



The Post-Huronian acid eruptives consist of granites, felsites, 

 syenites, and acid porphyries. Excepting toward the contact with 

 other formations, the porphyritic or felsitic phase is rare, and by far 

 the commonest species, both in the smaller bosses and in the main 

 masses, consists of an even and medium-grained granite of light 

 pinkish color. Though always weathered, it is often remarkably 

 fresh considering its antiquity. It is a much- sheared igneous rock, 

 but not so intensely so as are the igneous rocks which form so promi- 

 nent a part of the Lower Huronian schists. 



That these acid eruptives cut the Huronian rocks all along the 

 line of contact, and are hence later than these rocks, seems almost 

 undoubted, and though outcrops are often poor, owing to the quantity 

 of drift or the thickness of vegetation, still the eruptive contact of the 

 granite with the Huronian rocks is excellently shown in many places. 

 In the compass of this paper no detailed account of many interesting 

 contacts between the Huronian and the granitic rocks can be given. 

 Several representative instances may, however, be cited. Very 

 many points of contact were seen in which the irruptive nature of 

 the granite into the Lower Huronian schists is apparent. Perhaps 



