GEOLOGY AND NATURAL HISTORY OF LOWER CALIFORNIA. 977 



these beds and from calcareous layers about 200 feet above were 

 obtained the following forms, as determined by T. W. Stanton : 



Area breweriana, Gabb. Inoceramus, sp. undetermined. 



Baculites chicoensis, Trask, Ammonites, sp. undetermined. 



Tessarolax distorta, Gabb. Ostrea, sp. undetermined. 



" They correspond with forms found in the Chico beds of California 

 and Oregon. 



" From rolled pebbles of impure limestone obtained along the beach 

 to the south of the Playa, which had evidently fallen from the cliffs 

 above, and from a bed of similar composition in place at what was 

 assumed to be about 1,200 feet higher in horizon, at San Carlos anchor- 

 age (collected by A. D. Foote), 8 miles north of Bluff Point, the 

 following forms were identified by T. W. Stanton: 



Cardita planicostata, Lam. Tellina, sp. undetermined. 



Leda gnbbi, Conrad. Turritella, sp. undetermined. 



Urosyca caudata, Gabb. Dentalium, sp. undetermined. 



Nucula, sp. undetermined. Crassatella, sp. undetermined. 



and are considered by him to belong undoubtedly to the Tejon Eocene. 



"The beds carrying Chico and Tejon fossils were not observed in 

 direct superposition, but from the negative evidence that no decided 

 unconformities were detected at any of the points examined, it is 

 assumed that the two series are conformable, or that in any case no 

 considerable disturbance of the strata took place between the times of 

 their respective depositions. 



"The great mesa or plateau, 15 miles long and 6 to 8 miles in width, 

 which extends from the valley of Santa Caterina northward beyond 

 San Carlos, has an elevation of from 1,800 to 2,000 feet, being some- 

 what higher ^t the northern end. The greater part of its surface is 

 apparently capped by basalt flows, which have protected it from 

 erosion. From a distance can be distinguished conical points rising 

 above tlie level of the mesa, known as the " Sombrero," the "Hat," etc., 

 which resemble recent craters in general form. At one point on the 

 coast, fragments of the basalt, cemented together by crystalline calcite, 

 have fallen to the foot of the bluff in huge masses and form a projecting 

 point on the coast line. 



"For about a mile beyond Sandstone Point the beach is covered with 

 beautifully rounded pebbles of porphyries and a great variety of hard 

 rocks, mostly older eruptive, whose material must have come down a 

 ravine which drains the western face of the plateau and descends 

 very rapidly from its summit. As no such j^ebbles were observed in 

 the Chico or Tejon series, nor on the beaches to the south where no 

 upper beds remain, it is thought probable that the mesa sandstones, 

 which are characterized by an abundance of eruptive material, may 

 form the upper portion of this plateau. 



"Northward from San Carlos, as seen from the ocean or from com- 

 manding points of view in the interior, the same character of beds, 

 NAT MUS 95 62 



