248 



KUometres underlain by the readily eroded Cretaceous 

 rocks. The terraced alluvial filling of the 

 valley, where irrigated, is very fertile and 

 produces large crops of potatoes and other 

 vegetables. 



From the train one sees terraced out- 

 wash Glacial materials skirting the hills of 

 Cretaceous rock which are for the most part 

 capped by Tertiary lavas. The lavas of the 

 mesa-like hills are vesicular and amygdaloidal 

 basalts similar to those at Savona mountain. 

 The main type is a dense, bluish-black basalt 

 showing splendid ball-and-socket, as well as 

 columnar jointing. On the hill seen from the 

 railroad a few miles to the southeast of Ash- 

 croft, this basalt is found capping unconformably 

 a remnant of rhyolitic lava of probably Eocene 

 age. 



The topography in this portion of the Thomp- 

 son valley on account of the semi-arid nature of 

 the climate, approaches the 'bad land' type. 

 The hillsides are dissected by numerous small 

 gullies and ravines as a result of intermittent 

 but violent rainfall. 



One half mile south of the 50th mile-post, 

 after passing through the great landslide of 

 October, 1881, a gravel cut shows boulder clay of 

 the first period of valley glaciation, which here 

 underlies the clay silt and gravels deposited 

 during a later alluviation stage of the same 

 period. The railroad cuts through fissile Lower 

 Cretaceous argillites dipping steeply to the 

 west. The rocks at the western border of the 

 Ashcroft Cretaceous are more folded and dis- 

 turbed than those at the eastern border where 

 they appear to overlap the Jura-Trias rocks. 

 The total thickness of the formation is about 

 5,000 feet (1524 m.). A coarse basal conglom- 

 erate and grit member of the Lower Creta- 

 ceous is exposed in the rock cut immediately 

 north of the Black Canyon tunnel. 

 52-5 m. Black Canyon — The Thompson river here 



84-4 km. has incised itself, not only through a great 

 thickness of alluvium, but has also cut more 



