Ill 



detail is angular; and the batholith contains many in- 

 clusions of the intruded rocks, some of them recrystallized. 



The base of the mountain, as seen from the railway sta- 

 tion, is composed of massive granodiorite for the first 500 

 feet (152 m.) above the valley flat. Above are steeper 

 cliffs of interbanded sediments and intrusive porphyrite 

 sheets dipping to the west at about 30 degrees. The con- 

 tact is approximately horizontal, and the intruded rocks 

 are truncated by the batholith with little or no structural 

 disturbance. 



The granodiorite is a light-coloured, medium-grained 

 rock consisting of feldspar, quartz, biotite and hornblende. 

 It contains many dark inclusions and segregations varying 

 from 2 to 10 inches (5 to 25 centimetres) in diameter. 

 Some of these are angular and some are oval. The angular 

 ones are, without doubt, inclusions of either limestone or 

 quartzite. The rounded ones are recrystallizations and 

 may represent fragments stoped from the roof and re- 

 crystallized by the heat of the magma. 



The accompanying section illustrates the nature of the 

 contact, and it is noticeable that the acid contact zone is 

 thick in pockets in the roof of the batholith, while it is 

 comparatively thin or almost absent where a corner pro- 

 jecting down into the batholith forms the roof. 



On approaching the contact from below at one of these 

 pockets and at a distance of about 40 feet (12-2 m.) below 

 the roof, the granodiorite has its normal characteristics. 

 At 25 feet (7- 6 m.) from the contact there is a noticeable 

 change due to the partial elimination of the basic minerals, 

 and at 15 feet (4-5 m.) away these minerals are almost 

 entirely absent, and the rock becomes a fine-grained pink 

 variety made up largely of quartz, orthoclase, a little 

 plagioclase, and small flakes of biotite. A tendency to 

 porphyritic structure is also developed. Within three feet 

 (•9 m.) of the contact the change is most marked, and the 

 rock is noticeably more silicious. The porphyritic structure 

 is also well developed, the rock becoming a quartz porphyry 

 traversed by many small veins of guartz. The thin 

 section shows this rock to consist of phenocrysts of ortho- 

 clase and quartz, sometimes exhibiting a micrographic 

 intergrowth, in a fine-grained ground mass of the same 

 minerals also intergrown together in the same structure. 

 At the actual contact is about two inches (5 cm.) of perfectly 

 white, fine-grained, soft rock, now so decomposed as to 



