Geol.-Vol. I.] DA]'IDSOy— SUBMERGED ]' ALLEYS. 79 



mark this stretch of coast, there are no indications of sub- 

 merged valleys in this extensive plateau. 



The Columbia River Plateau. — From the latitude of 

 Tillamook Head, latitude 45° 58', the loo-fathom plateau 

 of the Columbia gradually sweeps out to 28 miles in breadth 

 off the mouth of the river, and then curves eastwardly toward 

 Shoalwater Bay, in latitude 46° 43'. 



III. Some Deep-Sea Soundings. 



Before describing the submerged valleys, it may be well 

 to notice a few of the deep-sea soundings in order to indicate 

 the rapid descent to the profound depths of the Pacific 

 plateau. 



Off the coast of Lower California: 2,000 fathoms off 

 Abreojos, in latitude 26° 45'. 



Off the coast from Point La Jolla to Point Pinos : 



1,000 fathoms at 37 miles W. SW. from San Diego. 

 1,900 " " 128 " W.byN. " " " 

 1,674 " " 34 " SW- " San Miguel Island. 



2,000 " " 35 " W. by S. " Point Conception. 



At 615 miles W. by S. from Point Conception is the sub- 

 marine mountain Belknap, which rises from 2,700 fathoms 

 to 388 fathoms. 



2,044 fathoms at 47 miles SW. from Cape San Martin. 

 2,000 " "57 " SW. by W. from The Sur. 



In other words, the depth of 2,000 fathoms is reached at 

 50 miles broad off the Santa Lucia range, and Cone Peak 

 of the outer range rises to 5,020 feet in lY^ miles from 

 the shore; thence northwardly the 2,000-fathom line trends 

 off the coast, and is 95 miles W. Y^ N. from Point Cypress. 

 It then approaches the coast off the Gulf of the Farallones. 



Outside of the lOO-fathom plateau, as we approach the 

 Gulf of the Farallones, the depth increases very sharply to 

 500 fathoms within two or three miles, and reaches 800 

 fathoms at 18 miles SW. from Santa Cruz; thence the slope 

 is more gradual. 



