i?. A. Daly — Secondary Origin of Certain Granites. 197 



comprises in succession coarse-grained red rocks, a fine-grained 

 red rock that is sometimes porphyritic and a well-marked belt of 

 altered quartzites. 



"The fine-grained red rock has all the characteristics of an 

 eruptive. It sends dikes into the contiguous bedded rocks, and 

 consists essentially of a hypidiomorphic granular aggregate of 

 plagioclase, anorthoclase and quartz. The quartz and anorthoclase 

 often form micropegmatite, while the plagioclase is in compara- 

 tively large grains, some of which have hardly defined idiomorphic 

 outlines. At a few places this red rock is porphyritic, with bipyra- 

 midal quartz crystals imbedded in a red granophyric groundmass. 

 The rock is similar to many of the augite-syenites described by 

 Irving as occurring in the Keweenawan series, and is in structure 

 and composition a quartz keratophyre. 



"The coarse-grained rocks between the gabbro and the kerato- 

 phyre are intermediate in character between these two. The 

 variety nearest the gabbro differs but slightly from the basic 

 eruptive. In addition to the gabbro components it contains a 

 little quartz and red feldspar — constituents derived from the 

 keratophyre. As the latter rock is approached, the augite, olivine, 

 and plagioclase disappear, while increased quantities of quartz, 

 red feldspar, and brown hornblende make their appearance, and 

 the rock becomes more and more like the fine-grained red rock. 

 Finally the hornblende disappears and the keratophyre is reached. 

 Since the intermediate rocks occur only between the gabbro and 

 the fine-grained red rock, and since all gradations in composition 

 between the two end members of the series are represented, the 

 coarse-grained red rocks are regarded as contact products formed 

 by the intermingling of the gabbro and the keratophyre mag- 

 mas."* 



After describing the compound external zone of contact 

 rnetamorphisrn, Bayley continues : 



" From the above-mentioned facts it is concluded that the con- 

 tact belt represents Animikie slates and quartzites that have been 

 altered near their contact with an intrusive rock. The rneta- 

 morphism of the quartzites has resulted simply in the recrystalli- 

 zation of the quartz and feldspar of the fragmental grains, with 

 the addition, perhaps, of a little orthoclase. 



" Since, in several instances, the gabbro is in direct contact 

 with the metamorphosed rocks, while the keratophyre is not to 

 be found in the neighborhood, it is inferred that the former rock 

 and not the latter was the cause of the contact action." 



The significant paragraph follows : 



"Inclusions of fragmentals in the gabbro and the keratophyre 

 have alike suffered the same alterations as have taken place in 

 the various members of the contact belt, with this difference, that 

 quartzite inclusions in the basic rock are often surrounded by a 



*W. S. Bayley, Bull. 109, U. S. Geol. Survey, 1893, p. 11. 



