Lawson.] 



Geology of Carmelo Bay. 



49 



that the delta is divided into two distinct portions by a sheet of 

 carmeloite lava, which has a maximum thickness of about 60 feet. 

 The edge of this lava sheet is well exposed, encircling the head of a 

 small, sharp canon which is being rapidly excavated out of the delta 

 material that underlies it. This small, sharp canon is held in on 

 either side by a granite ridge, and probably represents an old channel 

 of the San Jose. On the walls of this little canon the structure of the 

 lower or pre-volcanic part of the delta is well shown. The material is 

 stratified as a coarse conglomeritic sandstone, with a dip too steep 

 probably for an angle of deposition, even on the outer edge of a 

 delta, and the lava sheet is approximately conformable to this atti- 

 tude of the strata, thus suggesting a slight local disturbance. The 

 lava sheet, however, does not rest entirely upon the lower delta. 

 In part it reposes directly upon a level terrace-like ridge of the 

 Santa Lucia granite which has an elevation of 500 feet. This ter- 

 race-like ridge seems to be the remnant of an old sea terrace. The 

 lava sheet, where it rests upon the granite ridge, between the little 

 canon above mentioned and the gorge of the San Jose, is only a few 

 feet thick, but whether this rapid reduction in the thickness of the 

 sheet is an original feature or is due to subsequent stream action 

 could not be determined. 



From its lower edge the deita extends up the valley of the San 

 Jose for a known distance of over a mile, and it probably extends 

 much farther. At the distance of a mile up the valley, on the ridge 

 between the San Jose and the northern tributary, the delta is about 175 

 feet thick and reposes upon a floor of granite which has an elevation 

 of about 265 feet. This material is chiefly very irregularly bedded 

 incoherent sandstones and gravels. From its petrographical charac- 

 ters and its position it is thought to be the same formation as that 

 which nearer the ocean appears beneath the lava sheet. In fact, just 

 across the gorge of the tributary is a small patch of lava resting on 

 granite at an elevation just sufficient to cover this material if 

 extended; and it seems probable that a fairly large sheet of lava 

 has been removed in the process of the dissection of the deita. As 

 this delta material is well within the canon of the San Jose, with 

 high walls on either side, and is of great thickness (175 feet), it could 

 only have accumulated during a subsidence of the land. 



