19161 



Dickerson : 



Tejon Eocene of California 



397 



capped for a distance of more than a mile with the same gravel, which 

 half a mile from the quarry contains a layer of andesitic detritus. At the 

 extreme southwestern end of the ridge is a body of similar gravel, which 

 also rests plainly on sandstone of the lone formation. 



Occurrence of Eocene Fossils in the Ione 

 All the localities described by Turner have been visited. At the 

 last-mentioned locality, "the red sandstone quarry three miles south- 

 east of Buena Vista," the writer obtained Venericardia planicosta 

 merriami, Meretrix hornii Gabb, Psammobia, cf. hornii Gabb, Crassa- 

 tellites, sp., Turritella merriami Dickerson, Natica, sp., and Clavella, 

 sp. The Venericardia planicosta found here is the variety with the 

 obsolete ribs. All of these forms were collected from the sandstone 

 five to ten feet beneath the Neocene shore gravels. While the fauna 

 is a small one, it is typical of the uppermost, the Siphonalia sutter- 

 ensis zone of the Tejon. The sandstone member in this vicinity with 

 a dip of only one degree toward the west attains a thickness of 250 

 feet. It rests upon the clay, an altered rhyolitic tuff which is only 

 fifty to one hundred feet in thickness. This in turn rests upon the 

 steeply tilted eastward-dipping Mariposa slates of the bedrock series. 

 The same sandstone occurs on the hill east of Buena Vista Peak, 

 and with about the same thickness. A half mile east of the hill the 

 lower clay member becomes appreciably thinner and is only twenty- 

 five to fifty feet thick. On Waters Peak, one-half mile farther east, 

 the clay member and a good part of the sandstone member are miss- 

 ing and only the massive upper fifty feet of the sandstone member 

 is found resting upon the eroded surface of the Mariposa slates. 



The third member, the clay rock recognized by Turner, appears 

 to the writer to be merely a decomposition product of a rhyolitic 

 tuff. This rhyolitic tuff rests directly upon the sandstone member 

 in the vicinity of Buena Vista Peak. This is confirmed by an ex- 

 amination of the strata as exposed in Jones' Butte. A clay rock 

 was found resting upon the sandstone member. In certain places 

 this rock was found to be an unaltered rhyolitic tuff. 



From the above description it is seen that this formation appears 

 to have been deposited by a sea which transgressed from the west. 

 Two or more of the three members of the Ione are very persistent 

 over the Jackson Quadrangle, the Lodi Quadrangle, the Sacramento 

 Quadrangle, and the Sonora Quadrangle and they can be readily 

 recognized by their lithologic characters, low westerly dip, and 

 stratigraphic position beneath the andesitic tuffs and upon the Mari- 

 posa slates or other members of the bedrock series. 



