382 University of California Publications in Geology [Vol. 13 



rounded grains of magnetite are also present. The rock is altered 

 and considerable calcite forms a filling between the original constit- 

 uents. A specimen thirty feet higher is similar except that the feld- 

 spars are more acid, the phenocrysts being basic labradorite and the 

 ground mass andesine. 



A very dark greenish rock near the top of the section contains 

 grains and small granular masses of olivine which are prominent even 

 to the naked eye. Under the microscope it is seen to possess a typical 

 ophitic structure, laths of labradorite being imbedded in large tables 

 of augite. A considerable quantity of magnetite is present as small 

 blades. 



About three miles northeast of The Pipes there is a similar basalt- 

 capped hill, but here the lava rests directly on granite instead of on 

 sediments. As in the other case, there are many flows represented in 

 the mass. A dark purplish grey compact rock from near the top of 

 the hill contains abundant rounded phenocrysts of olivine. Large 

 laths of bytownite containing needles of apatite are also present. The 

 ground mass consists of small needles of labradorite with interstitial 

 grains of colorless augite ; also a considerable number of small grains 

 of magnetite. 



Resting on the fanglomerate on top of the ridge half a mile south- 

 east of The Pipes, there are several small areas of basalt. A dark 

 compact variety is so coarse that the striations on the plagioclase may 

 readily be seen in the hand specimen. Secondary calcite is present 

 as the filling of small cracks. Under the microscope labradorite and 

 augite exhibit an ophitic structure. The amount of augite, however, 

 seems to be small and the feldspars rather crowded. Euhedral grains 

 of olivine are rather prominent in the rock. It also contains numerous 

 blades of magnetite. 



On the ridge two miles south of the point where the Burns Canon 

 road crosses Antelope Creek, there are three small areas of basalt. 

 It is a very compact greenish-black rock containing grains of olivine 

 and also granular masses more than a centimeter across. Under the 

 microscope the small isolated grains are found to be euhedral and all 

 have rims of hyalosiderite. The ground mass consists of basic labra- 

 dorite microlites with considerable magnetite. Grains of augite are 

 also present. Two miles farther west there are two other small areas. 



South and west of Old Woman Springs there is a large area of 

 basalt. Just west of the springs and also a mile and a half southeast 

 low rounded knobs of granite project up through the lava. The north- 



