GEOLOGY OF THE PORT LEYDEN QUADRANGLE 1 3 



over pretty large areas and it is clearly the most homogeneous 

 rock mass among the Precambrics. The typical rock is a qnartz- 

 hornblende syenite alwa3^s showing the granitoid texture. The 

 quartz content varies a good deal but apparently without other- 

 wise affecting the rock. The dark colored minerals are always 

 very subordinate in amount. On weathered surfaces the color 

 of the rock varies from a light brown to a reddish brown, while 

 the color of the fresh rock varies from a sort of greenish gray 

 to a light gray. The rock is nearly always medium grained 

 although somewhat variable in this respect. In the field the 

 rock always clearly exhibits a gneissic structure which usually 

 can not be made out in the hand specimen. A distinct banding 

 is seldom shown except at times near the borders where the 

 syenite grades into the surrounding rocks. The minerals are 

 roughly arranged with their long axes parallel to the strike of 

 the foliation which ranges from n. 30° to 70° e. Such an 

 arrangement of the dark colored minerals causes the foliation 

 to be more evident, but they appear like wavy streaks which 

 are seldom continuous for more than a few inches or a foot. 

 The homogeneity of this syenite and its lack of distinct banding 

 serve to separate it from the other Precambric rocks in the field. 



The only noteworthy departure from homogeneity is to be 

 found in the presence of occasional small dark basic patches in 

 the syenite. These (patches nearly always show abrupt termi- 

 nations and to all appearances they are true inclusions. They 

 are rich in hornblende and biotite and are invariably arranged 

 with their long axes parallel to the gneissic bands of the syenite. 

 Such inclusions may be seen in the field southeast of Denley; 

 near where Miller brook enters the quadrangle; and probably 

 best in the large exposures southwest of Partridgeville. Most 

 of the syenite outcrops are, however, entirely free from such 

 inclusions. 



A number of syenite areas are shown on the accompanying 

 geologic map. Of these the southernmost one extends from 

 Denley southeastward to Hawkinsville and represents probably 

 the purest and most typical syenite of the region. Fine expos- 

 ures occur in the fields southeast of Denley and in the vicinity 

 of Hawkinsville. A large area extends from Miller brook north- 

 ward to Moose river with good outcrops along Fall and Miller 

 brooks; at Fovv^lersville and for 2 miles southward; and just 

 east of Lyonsdale. Another large area occupies the northeastern 



