422 B. WILLIS — SOME COAST MIGRATIONS, CALIFORNIA 



5,000 feet above the sea respectively. The spurs immediately east of 

 the crest and almost equaling the highest points in elevation consist of 

 a fine basal conglomerate of pebbles from the Coast complex and grade 

 rapidly eastward and stratigraphicall v upward into sandstone and shale. 

 These strata are very distinct from those of the Franciscan series out- 

 cropping a mile or two farther west. They are distinctly younger and 

 of comparatively simple structural character. In the opinion of Doctor 

 Fairbanks they are of Miocene age, since there is no* unconformity be- 

 tween these formations and the characteristic shales of the Monterey 

 formation overlying them. Some obscure fossils collected by Doctor 

 Fairbanks and Doctor Palache from this locality have not been carefully 

 determined. In this article the strata will accordingly be described as 

 Miocene (?) provisionally. 



MIOCENE (?) STRA TIGRAPHY 



Near the summit of the range the Miocene (?) strata have a steep north- 

 eastern dip, and descending eastward into the valley of the San Antonio 

 river one traverses a section of three distinct lithologie members in as- 

 cending order. The lowest is the basal conglomerate already referred 

 to as resting on the Coast complex, and continuous with it is an arena- 

 ceous formation consisting chiefly of coarse sandstone with some inter- 

 bedded shale. This formation is roughly estimated to have a thickness 

 of 800 to 1,000 feet. These sandstones are followed by several thousand 

 feet of dark gray shale with occasional interbedded sandstone layers, 

 and these in turn by several hundred feet of sandstone, which is coarse, 

 ferruginous, and at certain horizons conglomeratic. This stratigraphic 

 sequence presents a simple record of three steps : The first, a transgres- 

 sion of a sea upon an eroded surface of the Coast complex ; the second, 

 represented by the shales, a considerable subsidence of the sea bottom 

 with concurrent deposition of fine material ; the third, agencies of trans- 

 portation, so invigorated as to once more contribute the coarse sands and 

 pebbles to the sediment. 



GEOGRAPHIC CONDITIONS OF THE MIOCENE {?) 



A more detailed interpretation of the Miocene (?) stratigraphic record 

 may be suggested as follows : In striking contrast to the very coarse con- 

 glomerate at the base of the Franciscan formation is the comparatively 

 fine basal conglomerate of the Miocene (?) formations. The former con- 

 sists of pebbles many inches in diameter — rolled fragments of fresh rocks. 

 The other contains few pebbles as large as an inch or two across, and 

 includes numerous subangular bits of feldspar and quartz from decayed 

 rocks. Both conglomerates were derived from the Santa Lucia gneisses 



