Vol. XI] DICKERSON—PT. REYES AND SANTA ROSA QUADRANGLES 549 



be of the same age, but they have been somewhat arbitrarily 

 assigned to the Sonoma group because basaltic flows of con- 

 siderable extent are associated with them. 



This general distributional study of the Merced indicates 

 that the Merced was laid down upon a decidedly irregular 

 basement cut in Franciscan rocks, whose relief, judging from 

 the present elevation of Meachim Hill and the Franciscan area 

 at Cherry Station. Santa Rosa Quadrangle, must have been 

 400 to 500 feet. The surface does not appear to have been 

 wave-cut, but is apparently the result of sub-aerial erosion. 

 In other words, we are dealing with a peneplain which was 

 developed during Ep-Miocene time or Lower Pliocene time, 

 or both. The faunas of the Merced and its lithology indicate 

 that the shore-line of the Merced sea was near the present 

 northeast side of Petaluma Valley. 



FAUNA 



As was stated above in connection with the general descrip- 

 tion, the best collecting locality in the Merced group in the 

 region under discussion is at Wilson's Ranch, about one-half 

 mile east of Russian River. The fauna as listed below is 

 typically Merced, and beyond this the writer did not discover 

 any essentially new features. A study of this list readily 

 demonstrates that the locality from near the base of the Mer- 

 ced in this region near Freestone is typically Merced. 



DESCRIPTIONS OF LOCALITIES FROM MERCED (PLIOCENE) GROUP 



Locality 411. Interbedded fossiliferous s.s. with tuff on 

 ridge 3 miles SE of Freestone. Elevation 600'. 

 Same white sandstone overlying tuff. Dip 10° N 

 Strike E & W. Fossiliferous s.s. in Hall's ranch or 

 Burn's ranch. Schoolhouse in Burnside Dist. Sec. 

 17, T. 6. R. 9. Coll., J. B. Kerr, July 19, 1916. 



Locality 413. One-half mile north of Freestone and 200' 

 east of trestle in stream. Shaly s.s. and soft s.s. 

 Dip 5° S. Strike E. and W. 



Coll., J. B. Kerr, July 22, 1916. 



Locality 414. On Bodega — Valley Ford Road one-eighth 

 mile south of Bodega Post-office and Church. Dip 

 15° W. Strike N. 20° E. 



Coll., R. E. Dickerson, July 21, 1916. 



