Ransome.1 



The Great I 'alley 



415 



by the orogenic uplifts of the region. These valleys may not 

 always be synclinal in structure; some of the smaller ones may be 

 eroded anticlines; but, with few exceptions, the stream-watered 

 valleys of the state, having broad alluvial bottoms, are parallel with 

 the principal mountain uplifts, and are determined by them. There 

 is, of course, nothing remarkable in this. It is what occurs in 

 nearly all regions of parallel folding. But it is of interest to show 

 that the Great Valley of California is merely one member of a sys- 

 tem of valleys, and that most of the latter have certainly not sub- 

 sided isostatically. 



The considerable valley in which the Bay of San Francisco lies, 

 is, on the whole, as Professor Lawson has lately shown, a sunken 

 area. It resembles the Great Valley in gathering its drainage both 

 from its north and south ends, and in having a narrow western outlet, 

 the present Golden Gate, cutting directly through a range of hills. 

 The fact that the drainage from the Great Valley has always, as far 

 as we know, flowed across this now submerged valley of San Fran- 

 cisco Bay and through the Golden Gate, is some indication that the 

 two valleys have experienced substantially the same movements 

 during the Pleistocene, and that the present submergence of the 

 area covered by the bay is closely connected with the subsidence 

 indicated in the middle portion of the Great Valley by the borings 

 at Stockton. It therefore becomes important to decide, if possible, 

 whether sedimentary loading can be regarded as the cause of the 

 subsidence of the shores of San Francisco Bay. The latter is 

 undoubtedly an area of active deposition, but it is believed that any 

 geologist, even a believer in the theory of isostasy in its most 

 extreme form, would acknowledge that in this particular case the 

 amount of subsidence is in excess of that required by the theory. 

 As Professor Lawson has shown, the subsidence is not limited to 

 the immediate borders of the bay, but is discernible along the ocean 

 coast, from near Pigeon Point on the south, to Russian River on the 

 north, a distance of nearly 100 miles, and involving an area out of 

 all proportion to that immediately under load of recent sediments. 

 The bay itself presents a more conspicuously sunken aspect than 

 the mere weight of sediments laid down within it can account for. 



On the whole, then, it may be concluded that the maximum 



