4 



University of California. 



[Vol. 2. 



composed of the resistant Miocene flints, while on the southern 

 slope the bituminous shales are followed in descending order 

 by a great thickness of gypsiferous clays, in which broad valleys 

 have been eroded. Lower down toward the ocean the clays are 

 replaced by strata of volcanic ash, sandstone, and conglomerate, 

 in which, because of their greater resistance, canons have been 

 eroded. The strata of volcanic ash form very striking features 

 in the landscape on the lower slopes of the ridge; being interbedded 

 with soft clays, they weather out in cliffs and projecting ridges. 

 The streams cross a terrace, on emerging from the hills, which 

 widens toward the southeast. They have cut through the soil, and 

 in the case of the softer rocks have eroded their channels so that 

 they enter the ocean at a uniform grade, but where they cut across 

 the gabbro and serpentine, a fall occurs on the ocean cliff. The 

 canons of these streams give excellent sections of the strata from 

 the ocean to the summit of the ridge. 



The designation Lion's Head has been given to a picturesque and 

 precipitous mass of serpentine which rises very abruptly from the 

 water to a hight of 400 feet. 



OUTLINE OF THE GEOLOGY. 



Except for the area which forms the subject of this paper, the 

 line of hills terminating in Point Sal consists, as far as is known, of 

 Miocene and more recent strata. The region about the Point itself 

 has, however, been the scene of many violent disturbances and 

 repeated eruptions of basic magmas. A part of these consolidated 

 as surface flows, while others have the characters of deep-seated 

 rocks. 



The sedimentary strata comprise only the Pleistocene, Miocene, 

 and Knoxville. The Pleistocene forms a rim about the southern 

 slope of the ridge, the greater portion originally existing on this 

 side having been removed by erosion. On the northern slope it 

 forms a continuous sheet from the valley to the summit between 

 the ocean and Corralitos Creek. 



The Miocene is the most extensive formation represented. It 

 covers the greater part of the northern and eastern portions of the 

 area mapped. It is divisible into two distinct parts: the upper, the 



