Vol. 6] Merriam: Virgin Valley and Thousand Creek. 



37 



beds. The table-lands covered with this lava capping are known 

 to extend for a distance of fifteen or twenty miles north and 

 south. As seen from a commanding point above its level, the 

 table-land appears to have an extent several times the length 

 of the section in which the basalt capping has actually been 

 traced, and the presumption is that this How reaches over a 

 territory much larger than that personally visited. The surface 

 of the basalt cap, and of the mesas in general, is normally 



CANON RHYOUTE 



Fig. 3. — View of the mesa north of Beet Creek. See also plates 2 and 10, 



nearly level, or with only slight undulations. Several faults of 

 considerable magnitude have developed in the mesa to the 

 northeast of Virgin Valley in the movement of large crustal 

 blocks in comparatively recent time. 



To one traveling over the mesas, the surface of the tabli 

 presents a most unusual spectacle. The lava is only partly 

 covered by irregular patches of soil in which no plants larger 

 than sagebushes have developed. The evenness of the surface 

 and the unvarying nature of the long stretches of sagebrush 

 and lava blocks are such as to make a judgment of distance 

 most difficult. Above the surface of the lava there rise here 

 and there a few prominent points (see pi. 10), as Antelope 

 Butte (fig. 4, p. 41) situated on the mesa south of Virgin Valley. 

 This point consists of a dome of rhyolite which projects as an 

 island rising three hundred feet above the level surface of the 

 basalt How. 



The basalt sheet is near twenty-five feet in thickness over 

 the region where it has been examined, and consists of several 

 fairly distinct layers. The separate beds observed may not lie 

 persistent, and may be nothing more than local advances of a 

 single flow. The uniformity in thickness is quite remarkable, 

 and evidently indicates that the lava was poured out on a 

 nearly even plain. Though the dissection of the mesas by erosion 



