THE ONTARIAN SYSTEM PROPOSED. 1m 



Having these considerations in mind, it seems desirable, in the cause of the 

 concise expression of our knowledge and of the furtherance of clear and 

 simple conceptions of Archean geology, that the taxonomic value of this 

 upper division of the Archean should be recognized by the adoption of an 

 appropriate designation of systemic import. There is probably no other 

 equal area of the earth's surface Avhere the formations of this system are 

 better or more extensively exposed than in the Canadian province of Ontario. 

 The writer therefore begs to suggest to his fellow-workers in American 

 Archean geology that this system be known as the Ontarian System. 



Petro graphical Description. — The formations of different groups of the 

 Ontarian system present for the most part a sharp contrast in lithological 

 character and mode of occurrence to those of the Laurentian system. The 

 latter, as has been indicated, consists essentially of an assemblage of more 

 or less foliated or quite massive varieties of rocks which are to-day recognized 

 by petrographers as plutouic igneous rocks — e.g., granites, syenites, diorites^ 

 gabbros, etc. The former is composed of rocks which are with varying 

 degrees of certainty recognized as normal sedimentary and volcanic forma- 

 tions disguised by metamorphism of different kinds. Among the more easily 

 recognizable formations may be mentioned conglomerates, grits, quartzites, 

 graywackes, clay slates and limestones; various pyroclastic rocks, such as 

 ashes, tuffs and agglomerates; and massive volcanic rocks, both acid and 

 basic, notably quartz-porphyries and diabases ; all of which rocks, far from 

 beiug peculiar to the Archean, are normal constituents of Paleozoic and 

 later geological systems. In all of these, schistosity may be a feature of the 

 rock. 



With these normal or only slightly altered rocks occur also more highly 

 altered facies of the same formations, whose derivation is known, and others 

 still more differentiated from unaltered types, whose historical derivation 

 from normal rocks cannot be traced with certainty, but only inferred by 

 analogy as highly probable. Of those rocks whose original character is 

 more or less obscured, the most prominent are certain phyllites, mica schists 

 and feldspathic mica schists or gneisses, so called ; hornblende schists and 

 amphibolites, serpentines, soft, dark, glossy, green schists, and various light- 

 colored acid porphyroid schists, nacreous sericitic schists and felsitic schists 

 with quartz grains. These are all rocks upon which there has, in recent 

 years, been concentrated a great amount of research both in the field and in the 

 laboratory, aud many facts have been established concerning them in various 

 pares of the world which enable us to formulate definite and well-grounded 

 conceptions as to their origin and development, where formerly only more 

 or less indefinite speculation was possible. 



The rocks known as phyllites or phyllitic schists are very common in fos- 

 siliferous series in disturbed regions, and their clastic origin is -rarely ques- 



