1914] Dickerson: Eocene of the Santa Ana Mountains 



263 



in the lighter color of the matrix, in the firmer cementation, in the greater 

 abundance of pebbles of quartzites and slates, and in the occurrence of marine 

 fossils, both in the matrix and in the rounded pebbles. In the pebbles, frag- 

 ments of Inoceramus and an indeterminate gastropod were found, which might 

 imply that early Cretaceous strata had been removed by erosion. 



The gray conglomerate grades up into a coarse light-colored sandstone, 

 with an occasional band of hard, fine-grained calcareous sandstone, bearing a 

 characteristic fauna of early Chico Cretaceous age. Above this are six or 

 seven hundred feet of shale, laminated, and containing nodular layers of 

 limestone. The shale is followed by a coarse sandstone, in places decidedly 

 conglomeratic. Still higher in the series the sandstone is succeeded by a series 

 of alternating shales and sandstones. The uppermost Chico is characterized 

 by fine, hard, calcareous sandstones, conglomerates of a brick-red color, 

 micaceous sandstones, fine tan-colored shales and local pockets of carbonaceous 

 shales, in places yielding an inferior quality of coal. These uppermost beds 

 suggest a change from marine to brackish or land conditions. 



The thickness, considering those sections in which the entire series is 

 exposed, ranges from 1700 to 2500 feet, being greater to the northward where 

 certain sandstone strata become conglomeratic. 



The fauna is remarkable not only for the number of species but also for its 

 great vertical range. The abundance of fossils and excellent exposures afford 

 opportunities for fauna! studies in the Chico not before realized on this coast. 



Mr. Packard has recognized three and possibly four faunal zones 

 within these strata, and the fauna appears to show the presence of 

 both the upper and lower portions of the Chico. The lowermost zone 

 is characterized by Acteonella oviformis Gabb. The next zone in order 

 is characterized by the abundance of ammonites and Volutidae. The 

 abundance of a species of Turritella marks the zone which is found 

 in the middle of the section. Near the top of the Chico is found a 

 fauna which is marked by a scarcity of ammonites ; by the abundance 

 of pelecypods such as Meckia sella Gabb, Tellina matheivsonii Gabb. 

 and Tellina ooicles Gabb ; and by Perissolax brevirostris Gabb. a form 

 which generally occurs in the upper portion of the Chico. 



MAETINEZ GROUP 



Two small remnants of Martinez were recognized in this area, the 

 one being at Coal Mine Hill and the other two miles east of this 

 hill. The relations between the Martinez and the underlying Chico are 

 particularly well shown in the small area near Coal Mine Hill. At 

 this place the Martinez is separated from the Chico by a well-marked 

 unconformity. This is marked by great differences in dip and strike 

 and by abrupt changes in lithology. The strike of the Chico in this 

 vicinity is approximately N 15° E, with dip of 20° toward the west. 



