122 



which are themselves intruded by a body of Tertiary 

 granite. The youngest rock in the district is a flat-lying 

 flow of olivine basalt, covering a limited area to the south 

 east of Tulameen. 



The history of the region as recorded in the rocks may 

 be broadly summarized as follows: 



(i) Deposition of Triassic sediments and volcanics. 



(2) Mountain building and folding of the Triassic 

 rocks. 



(3) Batholithic intrusion of granite, peridotite and 

 pyroxenite, and granodiorite in Jurassic period. 



(4) Laramide revolution. 



(5) Eocene erosion period. 



(6) Extrusion of lavas, followed by deposition of coal- 

 bearing sediments in the Oligocene period. 



(7 Batholithic intrusion of granite in Miocene period. 



(8) Erosion period. 



(9) Extrusion of olivine basalt. 



(10) Uplift of Cascade mountains and Interior Plateau 

 in Pliocene times, followed by deepening of valleys. 



(11 Glacial period. 



(12) Post-Glacial uplift, and deepening of upper portion 

 of Tulameen valley. 



A variety of mineral deposits are found in the rocks of the 

 district. The Triassic rocks contain veins and replacement 

 deposits of gold and copper. Segregations of magnetite 

 and chromite occur in pyroxenite and peridotite. The 

 peridotite also contains both platinum and diamonds, 

 usually associated with the chromite segregations. Coals 

 are found in the sedimentary rocks of Oligocene age, and 

 ■ he placers of the district have yielded gold and platinum 

 in considerable amount. 



PLATINUM PLACERS. 



The principal streams in the district on which platinum 

 bearing gravels have been found are: Tulameen river 

 below Champion creek; Slate creek; Granite creek; 

 Newton creek. The gravels are post-glacial in origin, 

 and are found in the stream beds and on the sides of the 

 valleys at elevations not greater than 250 feet (76 •2m.) 

 above the streams. Except in Tulameen river below Slate 

 creek they are not of very great extent. All the payable 



