388 WincheU — Geological Age of the Saganaga Syenite. 



syenite of the Saganaga region. This phenomenon may be 

 seen at the end of a portage on Granite river, which forms 

 the international boundary line between Gnnflint and Saganaga 

 lakes. This band of silica is perfectly straight and so clearly 

 exposed that it is surprising that it has not been noticed before. 

 It has an east and west direction corresponding to the general 

 strike of the rocks in this region, and to the observed foliation 

 and coarse-bedded structure sometimes noticed in the syenite. 

 It stands vertically in the pink crystalline rock, and has along 

 one side a streak of greenish chloritic matter only a fraction of 

 an inch in thickness. 



The significance of this ribbon of chalcedonic silica in crys- 

 talline syenite may be more clearly perceived if we consider 

 the nature and origin of this particular kind of silica as eluci- 

 dated from the rocks of Keewatin age, and studied for several 

 years in northern Minnesota. The method of formation of 

 this peculiar variety of quartz has been outlined in a paper 

 entitled: "On a possible Chemical origin of the Iron Ores of 

 the Keewatin in Minnesota," by N. H. Winchell and H. V. 

 WincheU, read Sept. 2, 1889 at the Toronto meeting of the 

 A. A. A. S. 3 and has been treated in all fullness of detail as to 

 structure, chemical and petrographical characters in a forth- 

 coming bulletin of the Minnesota Geological Survey on the 

 Iron Ores of Minnesota. In the article and bulletin referred 

 to it is shown that this quartz, which forms the siliceous part 

 of the jaspilyte associated with the iron ore deposits, is amor- 

 phous and non crystalline. It is associated directly with rocks 

 of igneo-aqueous origin, and was formed by chemical precipi- 

 tation from heated oceanic waters at a very early stage of the 

 world's history. It mingles with the volcanic ashes and lavas 

 of the Keewatin in amounts varying from a fraction of a per 

 cent to almost absolutely chemically pure silica. It is a strik- 

 ing and unique characteristic of the rocks of the Keewatin age, 

 and has only to be seen to be recognized even in such peculiar 

 associations as in the Saganaga syenite. Wherever found it 

 indicates solution and oceanic deposition. 



Leaving chalcedonic silica for a moment, let us consider 

 another set of facts noticed in the Saganaga syenite area. On 

 the north side of Saganaga lake in Ontario, the rock compos- 

 ing the shore is found to consist largely of greenish feldspathic 

 and sericitic schists and agglomerates. The syenite passes into 

 these earthy schists directly, without the usual intervening 

 schists of the Vermilion age. So frequent and so varied are 

 the changes from syenite or chloritic syenite gneiss into thick 

 bedded or almost massive ?*idges of Keewatin rock that the 

 conclusion is inevitable that they are not separate formations, 

 but that the metamorphism of the schists has been more in- 



