PHYSIOGRAPHY OF THE BEAVERDELL MAP-AREA. 
11 
surface to structure, but not a marked one, and very often no 
apparent relation between rock structure and topography. 
Accordance between topography and rock structure is strongly 
indicated by the relations between certain upland valleys and 
fault zones in the rocks beneath them. Accordance seems 
proven also in certain areas where there is a marked difference 
in the topographic character of surfaces underlain by Miocene 
lavas and surfaces underlain by rocks of different texture which 
occur near the lavas (Plates III and IV). On the other hand, the 
general upland surface often passes over the contacts of rocks 
of different hardness and texture without apparent change in 
character. 
The relations between valleys on the upland and zones of 
fracture in the nearby rocks were studied more particularly in 
the Beaverdell area. Here it was seen that the valleys, both 
below and on the upland, are generally made up of straight 
stretches; that sets of these stretches were roughly parallel; and 
that any particular set might include both upland and deep 
valleys. Certain valleys below the upland were found to be 
actually following zones of fracture in the rocks, and certain 
valleys on the upland were lying in directions parallel to the 
strike of zones of fracture in the nearby rocks. Moreover, by 
plotting all the fractures observed by us on a protractor diagram, 
it was shown that they lie in roughly parallel sets and that the 
great majority of them trend from north to northeast. This 
is the trend of the larger number of parallel valley stretches. 
The general correspondence in trend between parallel valleys 
and parallel fractures, coupled with the fact that certain in- 
dividuals of a set of parallel valley stretches are actually known 
to follow zones of fracture in the underlying rocks, strongly indi- 
cates that the valleys both on and below the upland largely 
follow zones of weakness in the underlying rocks. In the Kam- 
loops area, and on other parts of the Plateaus, the same paral- 
lelism between valley stretches may be observed, and this 
suggests that the same conditions hold throughout the Plateaus. 
Changes in topographic form to correspond to changesjin 
the texture and hardness of the underlying rocks were seen^in 
the Beaverdell quadrangle. Certain lavas of Tertiary age 
