548 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



This general relation is further demonstrated by the occur- 

 rence of Merced fossils beneath the basalts of Burdell Moun- 

 tain. This hill rises to an elevation of 1560 feet and as the 

 map shows, its main mass consists of basaltic flows and tuff 

 beds of the Sonoma group. On the northwest end of Burdell 

 Mountain basalt, about a mile and a half south of Olompali 

 at an elevation of 300 feet, blocks of conglomerate containing 

 Merced fossils, Tivela crassatelloid.es (Conrad), were found. 

 These blocks, while not in place, were evidently derived from 

 a sandstone member which is exposed in a narrow creek canyon 

 in the vicinity. The Merced at this place rests upon Franciscan 

 rocks. Owing to slides, exposures in most places are meagre, 

 but only 50 to 100 feet occur here, as Dr. M. E. Blanchard, 

 who accompanied the writer to this locality, explored the 

 higher elevation immediately above the sandstones and shales 

 of the Merced, and found nothing but tuffs and lavas. From 

 the evidence we conclude that the lavas and ash deposits of 

 the Sonoma group were laid down close to the shore line of 

 the Merced sea. 



The Merced formation occurs in and around Penn Grove 

 and at one locality about one-half mile north of the village, 

 on the state highway, some casts of Merced fossils were col- 

 lected. The Merced outcrops in the village of Penn Grove 

 consist essentially of tuff and tuff-breccia, thus showing the 

 intimate relationships between the tuffs of the Sonoma group 

 and the marine Merced. Tan-colored sands and gravels en- 

 tirely surround Meachim Hill, whose top, however, is com- 

 posed of one of the Franciscan volcanics which is apparently 

 an olivine basalt. A mile and one-half southeast of Penn 

 Grove, Merced strata are in contact with the Petaluma for- 

 mation of Upper Miocene age. The contact unfortunately is 

 obscure but the inclination of the beds in the Petaluma for- 

 mation as exposed in Haggin Creek indicates that an angular 

 unconformity probably exists here. The general attitude of 

 the Merced beds is nearly horizontal, while those of the Peta- 

 luma formation exhibit dips as high as 12° to the southwest 

 in Haggin Creek. 



A series of tan-colored and tuffaceous sandstones is found 

 east and south of Lakeville. No fossils were obtained from 

 the beds, but they are assigned to the Merced upon lithologic 

 grounds. The basaltic conglomerates near Grand View may 



