Geol.— Vol. I.] DAVIDSON— SUBMERGED VALLEYS. 103 



is east, and the head is three miles north of the northern 

 island, and seven miles from the shore, which is a low ter- 

 race under high mountains. The soundings are too few 

 for minute illustration or description, but between two sound- 

 ings of 75 fathoms, one mile apart, north and south of each 

 other, the valley is 315 fathoms deep. This gives slopes of 

 1 ,440 feet in 3,000 feet, or about twice as steep as the heaviest 

 grades of the streets of San Francisco. 



The bottom is generally soft mud to 40 fathoms, although 

 there is occasionally sand as deep as 600 fathoms. Gray 

 sand and shells mark the bottom inside of 40 fathoms. 



