108 University of California. [Vol. i. 



highly siliceous character, which cannot be regarded as quite satis- 

 factory, and the conditions of their deposition and silicification must 

 be considered as a still unsolved problem. Near the eruptive 

 rock they have been much disturbed, but the general dip, near 

 the northwest corner of the map, seems to be in a southerly direc- 

 tion. The only satisfactory observation was that obtained at J, 

 where the bed crops out on the hillside as a ledge about fifty 

 feet long. The dip here is southerly, which would carry the jas- 

 pers under the sandstone to the south. Just outside the eastern 

 limits of the map the jaspers again outcrop, and the fact that this 

 second exposure is in the line of strike, has been deemed sufficient 

 warrant for the projection of the mapping across the doubtful dotted 

 area. \ 



Lastly, the sandstone is exposed again at the base of the hill on 

 the south shore of Rodeo Lagoon, but is too decomposed and soil- 

 covered to show dip or strike. It appears to be rather coarser here 

 than in the southern area, and shows evidence of shearing and dis- 

 turbance. Several angular fragments of jasper, about three inches 

 in diameter, were observed imbedded firmly in the sandstone, a fact 

 that militates against any theory calling for a general simultaneous 

 silicification of the whole jaspery series. Like the jaspers, this rock 

 again occurs just outside of the map, and presumably extends across 

 the intervening space, as mapped. 



The foregoing portion of the sedimentary series thus appears 

 to form a syncline, whose axis extends approximately northwest 

 and southeast. Of the southwestern limb of this syncline but a 

 small portion remains, the rest, as will be shown, having been dis- 

 placed by faulting. The jaspers do not reappear in the south- 

 western part of the map, but that they underlie the sandstone at 

 no great depth is indicated by the numerous inclusions of jaspery 

 fragments in the eruptive rock from the landing northward, and by 

 the occurrence of large loose blocks, bearing every mark of having 

 been included masses, lying on the beach just east of G. 



Relations to the Eruptive Rocks. — The diabase has been shown 

 to be intrusive into the sandstones and jaspers, and is, therefore, of 

 later age. The relative age of the spheroidal basalt is, however, 

 not so easily determined. Its present position is, undoubtedly, 



