GEOGRAPHIC CONDITIONS OP THE MIOCENE (?) 423 



and granites. The evidence is equally direct that the Franciscan coast 

 was abrupt and the Miocene (?) coast was plain. It also appears that 

 waves beat heavily on the Franciscan cliffs and lapped gently on the 

 Miocene (?) beaches. The proportions of the water bodies thus sug- 

 gested are as the Pacific ocean and the bay of San Francisco. 



The arenaceous formation which succeeds consecutively the basal 

 conglomerate of the Miocene (?) group is of small volume and arkose 

 composition. It is the product of erosion of a surface possessing only 

 moderate elevation and relief. 



The considerable mass of gray-black shale overlying the lower sand- 

 stone is sediment such as commonly gathers in estuaries similar to that 

 which now deposits in the southern portion of San Francisco bay. If 

 it be true, as will presently be suggested, that the Miocene (?) waters 

 were in this district bounded on the west by a land, then the geographic 

 place of this mud deposit may have resembled a larger San Francisco 

 bay. The great thickness of the formation accumulated during and in 

 consequence of equivalent subsidence. 



The carious brown sandstone and conglomerate overlying the shale 

 are in part probably not immediately derived from those crystalline 

 rocks which originally furnished the sand and pebbles, although, in so 

 far as the formation is an arkose, it does represent direct degradation of 

 decayed rocks of the Coast complex. The conglomerate, however, is 

 composed of pebbles of hard, enduring minerals, thoroughly rounded 

 and worn, which apparently have been more than once transported from 

 place to place of deposit. Together with the quartzose portion of the 

 sands, they may be detritus of a coastal conglomerate or of alluvial 

 cones. In contrast with the preceding sediment they indicate either 

 more vigorous subaerial transportation or more energetic wave and cur- 

 rent work, or both. By adequate study the significance of this member 

 and of the two preceding it may be fully deciphered. 



The structure of these Miocene (?) formations is that of a flexed mono- 

 cline, the dips from Cone peak being toward the northeast and ranging 

 from 70 degrees near the crest of the range to 5 in the eastern foothills. 

 The attitude is suggested in the sketched section, figure 1. Some dis- 

 tant views indicated that gentle synclines were formed by southwestern 

 dips about the head of San Antonio valley, but the observations were 

 not conclusive. 



RELATION OF THE MIOCENE (?) AND MIOCENE STRATA 



That range which has thus far in this paper been called Santa Lucia 

 is the western of two ranges which bear the name. The western extends 

 adjacent to the coast from point Sur to Morro bay (90 miles), where it 



