no 



stituent, associated with arsenopyrite in a gangue of quartz, 

 calcite, epidote, garnet, diopside, and other Hme-silicate 

 minerals. The ore bodies are of irregular shape and with- 

 out clearly defined boundaries. 



They occur in altered silicified limestone beds of Car- 

 boniferous age at the contact of intrusive sheets and dykes 

 of a light coloured gabbro, which appear to have emanated 

 from a central stock of the same material. They appear 

 to be genetically connected with the gabbro, and to have 

 been formed at the time of intrusion of that rock into the 

 limestone. The ore bodies being worked contain gold to the 

 value of about $ii.oo to the ton, and the mines are the 

 biggest producers of gold alone of any mines in British 

 Columbia. 



The deposits were discovered in 1894 and in 1904, actual 

 milling of the ores began and has since continued without 

 interruption. 



PARTICULAR DESCRIPTIONS. 



The chief points of geological interest at Hedley, which 

 it is the object of the excursion to visit are the following: 



(i) Roof contact of a granodiorite batholith, exposed 

 near the stamp mill of the Hedley Gold Mining company. 



(2) The Interior Plateau, to be seen from the top of 

 Nickel Plate mountain. 



(3) The Nickel Plate mine. 



Roof contact of Granodiorite batholith. 



An excellent section, showing the roof contact of a grano- 

 diorite batholith with tilted Carboniferous sedimentary 

 strata, is exposed on the northern side of Similkameen valley 

 east of the town of Hedley, and can be seen in a large 

 way from the railway station. 



The contact illustrates a case of differentiation in a 

 slowly cooling, igneous magma by the rising of the lighter 

 constituents, quartz and feldspar, to the upper surface of 

 the batholith, and the filling of pockets and fractures in 

 the sedimentary roof by these lighter constituents, where 

 they form aplite and quartz porphyry dykes and even 

 quartz veins. 



It also illustrates in certain features the theory of 

 batholithic intrusion by stoping; there is little structural 

 disturbance in the intruded rocks; the contact line in 



