Lawson ] 



Geology of Carmelo Bay. 



57 



There is no record anywhere on this part of the coast of formations 

 which can be referred, to the Pliocene other than those of the deltas 

 and terraces. No criteria have as yet been established for dis- 

 criminating between the Pliocene and the Quaternary in the coast 

 ranges other than palaeontological. Palaeontological (invertebrate) 

 criteria are unfortunately of little value for a discrimination between 

 rocks of such recent geological age. It is believed that a physical 

 distinction of some importance can be made between two sets of 

 geological conditions comparable to those of the Pliocene and 

 Quaternary respectively. This physical distinction may be ex- 

 pressed in the form of an hypothesis, subject to future scrutiny, 

 to the effect that the Pliocene corresponds to the period of more or less 

 continuous depression of the coast, till the land was at least 800 feet 

 lower than at present; and that the Quaternary corresponds to the 

 more or less continuous uplift which has affected the coast since the 

 maximum depression was reached. On this hypothesis the ancient 

 delta of the San Jose is a Pliocene formation and is to be correlated 

 with the Pliocene formations, also clearly of delta origin, which are 

 so largely developed a little to the south of the city of San Fran- 

 cisco. And the terraces of the coast, having been developed during 

 the recent uplift, are of Quaternary age. This hypothesis, it is per- 

 haps needless to remark, is in harmony with the accepted history of 

 events in the Sierra Nevada, even to the Pliocene volcanic activity. 

 The hypothesis implies, moreover, an important interval of high 

 altitude, similar to the present, and of great erosion between the 

 Miocene and the marine Pliocene. 



Submarine Valleys. — Our studies of the geology of Carmelo 

 Bay bring us in touch with the question of the submarine valleys 

 of the California coast. These valleys are of peculiar interest, be- 

 cause many of them end abruptly near the shore and have no cor- 

 responding rivers on the coast. Notwithstanding the absence of 

 corresponding land valleys, these submarine valleys have been con- 

 sidered to be submerged valleys of stream erosion,* the divorce of the 

 submarine valley from its landward prolongation and the oblitera- 

 tion of the latter being supposed to have been effected by orographic 



*See discussion of this subject byLeConte, Bull. Geol. Soc. Am., 1891, 

 Vol. 2, pp. 323-328. 



