246 



Kilometres ^ n one sec ti° n there is exposed to view about 

 1 50 feet (45 • 7 m.) of clay silt overlain by bouldery 

 till. The alluvium here is underlain by a 

 granodiorite batholith capped by a continuation 

 of the same series of Kamloops lavas. 



The contact between the granodiorite batho- 

 lith and the Jura-Triassic (Nicola) is near 

 the 43rd mile-post at a narrow part of the 

 valley. The Triassic limestones and intercalated 

 sheets of irruptive rock stand out prominently 

 across the river on the southeast flank of Rattle- 

 snake hill, where the series dips about 45 to the 

 northwest. 



The Nicola formation is overlapped from the 

 west by Cretaceous conglomerate, shale, and 

 sandstone — a formation which is encountered 

 first at the mouth of Barnes creek, where the 

 Thompson valley broadens out, preparatory to 

 taking a sharp southward bend in its course. 

 Here the river has been forced back upon the 

 delta of Bonaparte creek by the building out of 

 the Barnes Creek delta. The river has cut deep- 

 ly northward into the fluvio-glacial silts and 

 gravels west of Rattlesnake hill which stand out 

 in prominent cliffs about 300 feet (91 m.) high. 

 In one place, the stratified clay silts are seen 

 contorted and folded into a synclinal trough 

 which is filled by a younger and more sandy silt. 

 The younger silt was probably carried down and 

 deposited subaqueously by Bonaparte creek in 

 what was then a lake. The silts are believed to 

 be of two distinct periods of alluviation contem- 

 poraneous with two periods of valley glaciation. 

 The silts may be traced southwestwardly to- 

 ward the mouth of Bonaparte creek, where 

 boulder clay is found overlying the cross- 

 bedded gravels, sands and silts of the first period 

 of alluviation. The boulder clay is in turn 

 capped by a coarse river bed deposit with a 

 thin layer of silty soil on the surface of the 

 terrace. 

 47-2 m. Ashcroft. — Altitude 996 ft. (303.5 m.). 



75- 9km. Ashcroft, "the gateway to the north country", 

 is situated in a wide, level tract of valley land 



