The Siskiyou Island. 47 



through Queen Charlotte's sound all these 

 are but parts of the one continuous trough 

 that separates the Cascade range on the east 

 from the Coast range on the west. 



The incompleteness of this new coast bar- 

 rier was such that the ocean water had for a 

 long time free access to the Oregon part of 

 the depression, now the Willamette valley. 



The unity of movement, shown in the lines 

 of continuance of the mountain range and 

 the trough between this and the Cascade 

 range, presents several breaks; but these 

 broken links of the chain are explained by 

 the fact that the imperfection is always where 

 the new line of upheaval crosses an older up- 

 fold of the crust. 



In proof of this, notice that the California 

 part of the trough is interrupted by the older 

 uplifts over against the Siskiyou region; that 

 the trough which begins again in Southern 

 Oregon is interrupted by cross lines of earlier 

 upfolds, disturbing its development till it 

 crosses the Calapooia mountains, after 

 which, the trough, as the Willamette valley, 



