253 



KUometres much doubt. The writer regards them as Jura- 

 Cretaceous. These volcanic rocks, which con- 

 tinue as far as Thompson Siding, have, for con- 

 venience, been named the Spence's Bridge 

 group. They consist of a badly altered series, 

 chiefly of liparitic and andesitic lavas with 

 interbedded conglomerate, arkose and tuff, the 

 latter containing plant remains of Lower Creta- 

 aceous and Upper Jurassic age. 



A light yellowish member of the Spence's 

 Bridge Volcanic group is prominently exposed 

 below the mouth of Twaal creek, on the west 

 side of the valley, where the river begins to 

 take a westward course. This is a peculiar 

 acidic lava, with spherulites averaging f inch 

 (i cm.) in diameter and having in places pro- 

 nounced flow structure. The acidic lavas are 

 intruded by basic dykes, possibly the feeders for 

 the younger Miocene basalts. 



One mile above Spence's Bridge the broad 

 glaciated valley of the Nicola joins that of the 

 Thompson. 



72 • 6 m. Spence's Bridge — Altitude 768 ft. (234 • o m.) . 

 1 16 -8 km. Spence's Bridge, the junction point for the 

 Nicola Valley railroad, is picturesquely situated 

 in Thompson valley at the base of the precipit- 

 ous Arthur's Seat mountain. 



Arthur's Seat, rising abruptly 5,500 feet 

 (1,676 m.) above sea level, is thought to have 

 been one of a series of volcanic vents which 

 were active along the east front of the 

 Coast range in Jura-Cretaceous time. At the 

 base of Arthur's Seat may be seen silt escarp- 

 ments, from which a large volume of alluvium 

 broke away on Aug. 13, 1905, damming the 

 Thompson river and causing the destruction of 

 an Indian village across the river. Five Indians 

 were buried alive in the slide, ten were killed 

 and thirteen hurt by the wave which swept 

 up the river. 



79-1 m. Drynock — Altitude 752 ft. (229-2 m.). A 



127-2 km. few miles below Spence's Bridge, the narrowing 



valley swings southward and maintains a 



