EAELIER TERTIAKY (EOCENE AND OLIGOCENE). 751 



from observations at a distance the lower lavas seem to be not so basic as the upper ones, which 

 are chiefly olivine basalt. A single specimen of biotite andesite was all that was collected to 

 represent these more siliceous volcanics. 



Near the summit of the pass, just east of Furnace Creek, there come in above the yellow- 

 green Tertiary series softer dark-brown honeycombed conglomerates, recalling the similar rocks 

 of Meadow Valley Canyon. Thin sheets of basalt are interbedded with the conglomerates, 

 but the great sheets lie on top. Patches of this same upper conglomerate series were elsewhere 

 observed, and at one place its contact with the underlying yellow-green series appeared slightly 

 discordant. The conglomerate contains pebbles and bowlders which are chiefly of lava and 

 must have been derived from the sheets of basalt which were periodically poured out during 

 the deposition of the beds. 



A rough estimate of the thickness of this whole series of slightly consolidated beds and 

 volcanics puts it at not less than 4,000 feet and the nature of the sediments shows that they 

 must have been deposited in standing water. The presence on some of the beds of gypsum, 

 borax, and calcareous tufa shows that at some periods the waters in which the sediments were 

 deposited were evaporated. They were, therefore, those of an inclosed lake, which was prob- 

 ably of great dimensions. It is likely that a large' portion of the beds were deposited in fresh 

 water at a period different from that in which the chemical precipitates were laid down. 



The borax in these beds is probably contemporaneous with the borax deposits iii similar 

 folded Tertiaries at Daggett and elsewhere in the Mohave Desert. Between these two locali- 

 ties, moreover, the strata, so far as known, appear to be roughly continuous. The strata of 

 Mohave Desert are exposed on a grand scale at Cajon Pass, where they contain beds of black 

 lignite. 



Northward from Furnace Creek, at Silver Peak, are found beds of the Esmeralda forma- 

 tion, which are entirely similar in nearly every respect to those at Furnace Creek. Moreover, 

 the fossils found in the Esmeralda beds indicate a nearly similar age to that indicated by 

 fossils found in the Tertiary strata of the Mohave Desert, just west of Cajon Pass. 



The upper part of the Furnace Creek beds is identical in appearance with certain semi- 

 indurated and shghtly folded conglomerates and sandstones found in Meadow Valley Canyon, 

 which have been referred to the Pliocene. 



J 10. SACRAMENTO VALLEY AND COAST RANGES, CALIFORNIA. 



The general relations of the Eocene of the Pacific coast to the underlying 

 strata are thus stated by Arnold:" 



A widespread unconformity exists between the Eocene and the Cretaceous on the Pacific 

 coast of North America. Throughout Washington, Oregon, and certain parts of California 

 this unconformity is angular, while over considerable areas in California and at one locality 

 in Oregon the unconformity may only be recognized by a more or less marked hiatus in the 

 faunas. 



It is a noteworthy fact that wherever the line between the marine Eocene formations 

 (Martinez, Arago, Tejon, etc.) and the Cretaceous beds is marked by an angular unconformity, 

 the underlying beds are either of lower Cretaceous (Knoxville) or middle Cretaceous (Horse- 

 town) age, and that wherever the Eocene rests on the Chico, or upper Cretaceous, with the 

 one exception at San Diego, the unconformity is not angular and, as far as the stratigraphic 

 evidence goes, the two formations represent an apparent uninterrupted period of sedimentation. 



The apparent conformability of the Eocene on the Cretaceous, together with the super- 

 ficial similarity of their faunas, led Gabb and Whitney, of the early California Survey, to class 

 the Martinez and Tejon formations with the Cretaceous. White, Stanton, and Merriam have. 



