Geol.— Vol. I.] DAVIDSON— SUBMERGED VALLEYS. 77 



of the Cascade Mountains, but through a long gorge in the 

 basalts, about six miles wide. This river drains a very 

 extensive region, and it brings down immense deposits of 

 detritus, which have formed a comparatively broad plateau 

 of 28 miles within the lOO-fathoms depth. In this plateau 

 are evidences of a submerged valley, but further details are 

 needed to determine its peculiarities. 



4. Columbia River to the Strait of Fuca. 



Northward of the Columbia River the coast-line is in 

 great measure low and backed by distant mountains, the 

 outlying flanks of the Olympus mass. 



Nearly halfway from Cape Disappointment (287 feet) 

 these spurs gradually approach the shore until they reach 

 Cape Flattery, with an elevation of about 1,500 feet. In 

 this stretch of 125 miles of coast empty the waters of Wil- 

 lapa (formerly Shoalwater) and Gray's Bays, and two or 

 three streams from large lakes inland : but there is no sign 

 of a submerged valley abreast this low region. The sound- 

 ings are relatively shoal for 20 miles off shore. That great 

 inlet, the Strait of Fuca, opens upon the ocean in latitude 

 48° 23''-48° 31', with the high island of Vancouver forming 

 the north shore. The strait lies nearly east and west for 

 eighty miles, with an average width of ten or twelve miles. 

 It has an average depth of 100 fathoms in mid-channel, with 

 150 fathoms at the mouth, and a sharp turn to the southward 

 parallel to the shore for some miles. It is the channel way 

 for all the tidal waters of the far-stretching arms of Puget 

 Sound on the south, and of Washington Sound and the Gulf 

 of Georgia on the north. 



II. The One Hundred-Fathom Plateau. 



Off this long, bold coast thus briefly described, the waters 

 of the Pacific reach a depth of 2,000 to 2,700 fathoms 

 within as little as fifty miles off the mountain flanks. The 

 descent to these profound depths is not uniform, however, 



