750 INDEX TO THE' STRATIGEAPHY OF NORTH AMERICA. 



I-J 11. GREAT BASIN, NEVADA ANB CALIFORNIA. 



The Esmeralda formation ^^* occurs in southwestern Nevada along the base of 

 the Sierra Nevada in the ranges developed by later Tertiary movements. ' It is 

 tentatively assigned to the Oligocene and described as a lake deposit. Its general 

 character appears to place it among the continental deposits of mixed character. 

 The southern portion of the Great Basin, lying in southeastern California near the 

 Nevada line, comprises Death Valley and the adjoining ranges, which are composed 

 largely of Tertiary strata. Spurr "^^ says: 



In the eastern part of the [Grapevine] range, where the road crosses from the Amargosa 

 Valley into Furnace Creek, there is found a great amount of conglomerate, forming high hUls. 

 These conglomerates are very coarse and contain rounded pebbles and bowlders of all sizes, 

 made up of reddish and white quartzite and black and gray limestones bearing the badly pre- 

 served Paleozoic fossils above mentioned. The conglomerate is as hard and firm as the rocks 

 from which it is derived. It is water-laid and well stratified and evidently a shore formation. 

 The whole thickness exposed is estimated at 4,000 feet. It .is sharply folded, together with 

 the limestones from which it is derived, but it abuts abruptly against these limestones on 

 the west. 



The irregularity of the contact between conglomerate and limestone denotes a great erosion 

 interval, yet no unconformity of attitude is apparent. 



This conglomerate seems to fringe the north edge of the bold Paleozoic scarp of the Grape- 

 vine Mountains across the greater portion of the range. It is found at various points. A little 

 west of Pyramid Peak conglomerate occurs, interbedded with and Tunning laterally into a hard 

 limestone, which has all the appearance of being calcareous tufa. A specimen examined micro- 

 scopically bears out this idea and sho^V^s that the rock is probably a chemical precipitate. It 

 is like a rock found in crossing the Panamint Range from Death Valley to Windy Gap, and 

 also like one from the Esmeralda formation, between the Candelaria Mountains and the Pilot 

 Range. 



Besides these rocks there occur, as parts of the same series, semiconsohdated gravels, with 

 clays partially hardened to slaty shales, limy clays partially consolidated to argillaceous sec- 

 ondary limestones, and sands partially hardened to cherty and limy sandstones, all interbedded. 

 All these, including the conglomerate and the limestone tufa, have a general light-yellow, often 

 greenish color, characteristic of the. series. 



This sedimentary series makes up the greater portion of the Funeral Range. Along Fur- 

 nace Creek valley and on both sides of it the mountains consist chiefly of yellow-green strata 

 capped by basalt. The lava seems to occur interbedded with the sedimentaries, as well as 

 overlying them. The series is here consolidated into a hard clay rock, with occasional thin 

 sandstone, and the general yellow-green color is changed in places to reddish, yellowish, and 

 pinkish. The rocks are often gypsiferous and contain abundant grass remains, which are, 

 however, indeterminable. From the yellow-green Tertiary series in the hUls just east of the 

 mouth of Furnace Creek there has been taken much borax, which occurs as borate of lime in 

 beds in the strata. * * * 



On the eastern side of Death Valley, southward from Furnace Creek, the upturned yellow- 

 green Tertiaries, with some few intercalated sheets of lava, constitute the mountains. Beneath 

 some of these sheets the clays are baked to a red, natural brick. The lavas seem to occur chiefly 

 at the top of the yellow-green series, or at a still higher horizon, for the great mass of beds 

 exposed in the lower portion of Furnace Creek contains no lava sheets; yet in these beds occur 

 occasionally lava bowlders and pebbles, so that we conclude that the period was one of con- 

 tinual volcanic activity. From fragments of lava picked up at the base of the mountains and 



