39 6 



University of California. 



[Vol. 2. 



cision. It will be sufficient to say that we do not reach the base of 

 it even when we descend to San Pablo Greek, and that it reposes 

 unconformably upon the Monterey formation in the hills on the 

 east side of San Pablo Valley. As we follow the Orindan forma- 

 tion thus easterly, we find it not only thicker but affording evidences 

 of a deeper water sedimentation. Conglomerates still form a large 

 proportion of the whole accumulation, but there is a larger propor- 

 tion of evenly-bedded and finer-grained sandstones, shales, and 

 clays, There are also several thin beds of limestone and thin beds 

 of dark volcanic tuff intercalated with the shale and clay beds, 

 which are not represented on the southwestern limb of the syn- 

 cline. The fine-grained sandstones, shales, clays, and limestones 

 are characterized, as has before been stated, by an abundance of 

 fossil fresh-water ostracods,* and these crustaceans are practically 

 the only invertebrate fossils which are known to occur in these 

 rocks. 



Subordinate Flexures. — The Orindan beds beneath the amyg- 

 daloidal andesite when we first meet them in our descending sec- 

 tion on the slopes north of Eureka Peak, dip to the southwest 

 conformably with the sheet of andesite. But the dip rapidly 

 changes, as may be readily observed in the excellent exposures on 

 the north side of the first ravine north of Eureka Peak. The 

 stratified gravels are here seen in the face of the bluff to pass from 

 a southwesterly dip to a northeasterly, forming a perfect anti- 

 clinal arch. From the crest of the arch the overlying andesite 

 has been almost entirely removed, leaving only a residual patch a 

 few yards in extent. The dip on the northeastern limb of the 

 anticline conforms closely to the slope of the hill, but is sufficiently 

 steep to again carry the conglomerate beds beneath the andesite. 

 This anticline is quite a minor feature compared with the great 

 syncline which dominates the structure of the Berkeley Hills. It 

 is, however, longitudinally persistent along the entire slope within 

 the limits of our map. 



Immediately to the northeast of this anticline there is another 

 shallow syncline of still less importance than the anticline. It is 



*See Bull. Dept. Geol. I'niv. Cal., Vol. 2, No. 2, on Some Pliocene Ostra- 

 coda from Near Berkeley, by Frederick Chapman. 



