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University of California. 



[Vol, 



by the fact, drawn from a more general study of the region 

 beyond the Berkeley Hills, that other formations, such as the 

 upper part of the Monterey series and the San Pablo formation, 

 which normally occupy this interval, are here lacking. 



The basal beds of the Orindan formation are pebble-conglom- 

 erates, and their actual contact against the Monterey formation is 

 well exposed on the lower two-thirds of the south slope of Sky- 

 line Ridge. The conglomerate bed is well cemented and affords a 

 prominent outcrop showing a vertical dip, and the attitude of the 

 plane of contact is clearly vertical. The bedding of the cherts is, 

 however, not satisfactorily exposed. On the south side of Monu- 

 ment Hill the contact is again perfectly observable and here the 

 bedding planes of the chert are better exposed than those of the 

 conglomerate, and are seen to abut obliquely upon the contact plane, 

 so that it is quite apparent that the conglomerates rest upon the 

 basset edges of the chert beds. On the side of the ravine beyond 

 Monument Hill a quarry has been opened in the chert formation 

 for the purposes of obtaining road metal. The opening is close to 

 the contact, which is again about vertical, and in the quarry face it 

 is apparent that the chert and shale beds are intensely deformed, 

 being, in fact, contorted and sheared in an intricate way, while there 

 is no evidence that the conglomerates are so affected. They 

 appear to lie across the abraded edges of the contorted cherts. 



In the next transverse ravine the contact plane between the two 

 formations presents an abrupt jog, which can only be interpreted as 

 the heave of a fault which lies in the line of the creek. The 

 extent of the heave is about 200 feet. Beyond this fault, to the 

 northwestward, the plane of contact between the two formations 

 gradually changes from a vertical attitude to a southwesterly dip, 

 so that the beds of the Monterey formation appear to lie upon the 

 Orindan formation, thus reversing the natural relations of super- 

 position. This inverted dip both of the chert strata and of the 

 contact plane is quite apparent on the last transverse ridge over 

 which the contact is traceable, the angle of dip being variable but 

 having an average value of about 70 . A little beyond this the 

 entire Orindan formation is cut off by the Canon fault just as the 

 Monterey is. 



