PLIOCENE FORMATIONS. 29 



DEFIMTIOX. 



The type section of the Merced formation consists of a series of rather soft, 

 gray sandstones and sand\' shales, interbedded with hard pebbly conglomerates, 

 hard well-t'eniented shell layei's, and occasional lignitic seams. The total thick- 

 ness of the formation is approximately 5,000 feet. In age the Merced probably 

 represents the upper Pliocene and lower Pleistocene, although there is no appar- 

 ent unconformity in the type section, which is certainly Pliocene at the Inise and 

 Pleistocene at the top. 



LOCALITIES. 



Mi/liluK beds, Shoalwater Bay, Oreg. (Dall, 1898, p. 336). 



Ujiper portion of the "Wildcat formation," Eel River, Humboldt County (?). 



8ea cliffs south of Lake Merced and foothills between tliem and Twelvemile Creek; north of 



Pillar Point; uppermost Ijeds in sea cliff at mouth of Alio Nuevo Creek, San Mateo 



County. 

 Felt Lake, near Stanford University, Santa Clara County. 

 Uppermost beds at Capitola, Santa Cruz County. 

 Beds at Bath House Beach and at least a portion of Packards Hill beds, Santa Barbara, Santa 



Barbara County. 

 Old irrigating ditch north of \'entura, Ventura County. 

 Pliocene and lower portion of San Pedro formation, Deadman Island and San Pedri.i; Santa 



Monica Canyon, Los Angeles County. 

 San Juan Capistrano, Orange County. 

 ITpper portion of San Diego formation, Pacitic Beach, and San Diego, San Diego County. 



FAUXA. 



The fauna of the lower beds in the Merced formation indicates clearly their 

 Pliocene age, while at the top the fossils show the Pleistocene origin of this 

 part of the formation. In using "Merced" in its bi-oader sense as a horizon 

 name in the California column it is deemed advisable to confine it, in a general 

 wa_v, to that period of the standard geologic scale (viz, the Pliocene) to which 

 the great bulk of the sediments of the formation belong. In correlating, 

 however, the ecjuivalence of the lower portion of the next higher formation (the 

 San Pedro) to the upper portion of the Merced should be borne in mind. 



Pecten faima. — No Pectens have so far been recorded from the type section 

 of the Merced, although beds of probable equivalent age to the Pliocene portion 

 of it have 3'ielded the following species: P. ashleyi, P. leNux, P. hdl/lamellatus, 

 P. caicrtiiufi, P. cerrosertsis, I'. Cdoperi^ P. {Hhiniies) giganteus, P. hadutuH and its 

 varieties hericiiis, hindmi, nararchus, and sfrategKn, P. healeyi, P. hem])hilU, P. 

 /'shuuliciis, P. jordani, P. laficnirifus, P. ojyiiritia^ P. parmdeei, P. rivers!, and 

 P. stearnsii. 



The following fauna has been found at or in the immediate vicinity of the 

 type locality of the Merced formation, and may be taken as characteristic of the 

 horizon represented by the whole formation: 



