210 University of California Publications in Geology [Vol. 10 



conditions. It is believed, therefore, since such conditions undoubt- 

 edly frequently obtained in the Etchegoin, that the beds of gypsum 

 were deposited, at least in part, in basins isolated from the ocean, in 

 fresh-water lakes, or on a periodically flooded delta at the time of 

 deposition of the Etchegoin. The climatic conditions under which this 

 deposition took place were probably arid. 



LIMESTONE 



Along the divide between Jacalitos Creek and Salt Creek, about 

 one-half mile east of Robert's ranch-house, a limestone bed outcrops. 

 On megascopical examination the bed is found to be compact and 

 massive in the middle, but the upper and lower portions are lami- 

 nated. These laminae are very thin, being not over 2 mm. in thick- 

 ness. On examination with a petrographical microscope a few minute 

 grains of quartz were observed. The bed both above and below grades 

 into sandstone typical of the formation. It has a thickness of about 

 ten feet and is traceable about one-half mile until intersected by 

 faults. "With coarse sandstone above and below containing fossils 

 indicative of a shallow marine origin, the conditions necessary for 

 deposition of limestone in the ocean were probably not present. The 

 conclusion is therefore reached that the limestone may have been 

 deposited under some such conditions as might obtain in a temporary 

 lake, or in an estuary temporarily severed from the sea. 



Invertebrate Fauna 



INVEETEBEATE ZONES 



Four distinct faunal zones have been recognized in the Etchegoin. 

 No fossils have been found near the base of this group. The lowest 

 important fossiliferous horizon is the Chione .elsmerensis zone, in 

 which C. elsmerensis English is abundant. This faunal association 

 extends through several hundred feet of strata in the middle portion 

 of the lower Etchegoin and is typically that of the lower Etchegoin, 

 or "Jacalitos," as described by Arnold and Anderson. Several of 

 the species are unknown outside of this area. The occurrence in these 

 beds of C. elsmerensis English, C. fernandocnsis English and several 

 other forms shows that its closest correlative is found in the lower 

 Fernando near Newhall, Los Angeles County. The typical faunal 

 assemblage of this zone may be found at locality 2526. Among the 

 characteristic species may be mentioned Astrodapsis jacalitosensis 



