1907.] 



CRANDALL— SAN FRANCISCO PENINSULA. 



15 



over a mile in thickness. The beds are only partially consolidated 

 except locally. The series consist mostly of sands and clays bedded 

 from a few feet to over a hundred feet in thickness. Certain thin 

 conglomerate layers are much harder and more resistant than others ; 

 these consist of jasper pebbles and broken shells. This hard con- 

 glomerate is well exposed at Alussel Rock and along the ridge 

 southeast of there, lying along and near the Franciscan rocks. 

 There are dark or almost black clay beds in the series and these 

 are the ones that are most fossiliferous. As the upper part of the 

 section is approached the beds are softer and more sandy. There 

 are a few small layers of lignitic material and in the cliffs just 

 south of the Life Saving Station there is a layer of white volcanic 

 ash. Along the cliff this layer of ash has a fairly constant thick- 

 ness of ten or twelve inches. 



Dr. Ashley has described these beds more thoroughly and has 

 given their identification in his paper. ^ 



IV. Post-Pliocene. — Above the Merced series lies the Pleisto- 



FiG. 6. 

 Pleistocene and recent deposits overlying the serpentine of the Presidio sil 



■ Neocene Stratigraphy of the Santa Cruz IMountains, Proc. Cal. Acad. 

 Sci., Series 2, V, 312. 



