Winchell — Geological Age of the Saganaga Syenite. 389 



tense in certain belts of country, and the syenite is simply the 

 result of this intensity. This phenomenon of locally intensi- 

 fied metamorphism may be easily accounted for if we remem- 

 ber that pressure alone cannot develop heat, but pressure 

 together with motion produces intense heat at tfye planes where 

 the motion takes place.* Thus if the Keewatin strata at 

 Saganaga were folded at an early period, so as to stand np 

 vertical, the lateral pressure would not effect one portion of 

 the rocks more than another. But if this lateral pressure were 

 accompanied by a slipping of some ridges up and of others 

 down, the result would be ridges slightly altered alternating 

 with highly metamorphosed Keewatin strata. For a space of 

 several miles along the north side of the lake this condition of 

 affairs is noticeable. The ridges of Keewatin green schist, and 

 of syenitic rock rise in bare alternating or intermingling ranges 

 of varying width and altitude, but generally of such narrow 

 width, that there are half a dozen such transitions in the space 

 of a quarter of a mile. At a short distance it is impossible to 

 say whether the rock ahead is more like Keewatin green schist 

 and agglomerate, or the syenite peculiar to the southern half 

 of the lake. The agglomeritic structure is almost universal in 

 the hills a short distance north of the lake shore, and suggests 

 again the idea that the wonderful syenite conglomerate may be 

 only a Keewatin agglomerate highly altered locally. This is 

 not at all unreasonable, for the bowlder forms in the green 

 schist are neither so much altered structurally by the assorting 

 agency of the ocean in which they fell as volcanic bombs, nor 

 so acidic by reason of the intermingled chalcedonic silica as the 

 surrounding rock, and hence would remain as green u pebbles " 

 under metamorphism sufficiently intense to convert the matrix 

 into syenite. 



The presence of chalcedonic silica in the Saganaga syenite 

 together with the structural relations existing between the non- 

 crystalline Keewatin schists, and the crystalline syenite supposed 

 to be of Laurentian age amount almost to conclusive proof that 

 the materials of which the syenite is composed are not Lauren- 

 tian but Keewatin in age. The presence of the numerous and 

 large quartz grains mentioned above as being characteristic of 

 the syenite of the Giant's Range may now be easily explained 

 when we consider the immense amount of chemically deposited 

 chalcedonic silica in the Keewatin. The same metamorphism, 

 which by hydro-thermal fusion and pressure formed the ortbo- 

 clase and hornblende from the other ingredients has been suffi- 

 cient to crystallize most of the silica into large grains. 



* 0. Fisher, Physics of the Earth's Crust, 1889, p. 2. 



