..-.lUARY 20, 1905.] 



Now it is a remarkable fact that the 

 white sands, thirty or forty miles off to the 

 northeast, exhibit an almost identical flora. 

 The student hastens across the intervening 

 desert to meet that shining wall, expecting 

 to find all things new; but, behold, the 

 white sands are sands first of all rather 

 than anything else. Whatever their chem- 

 istry, and they have their peculiar prob- 

 lem for the chemist, only a vegetation that 

 can endure a moving, shifting terrene can 

 flourish here. The white sands form, ac- 

 cordingly, part of the yucca desert. Their 

 relation to vegetation is almost purely 

 physical, but they exhibit some peculiar- 

 ities. They are gypsum, as everybody 

 knows,* but while they move as other sands, 

 they must be compared with wet sands; 

 the vast drifts, thirty to fifty feet in height, 

 are moist often to within a few inches of 

 the surface, and are so compactly driven 

 that one may walk upon the solid surface 

 Avith comparative ease. A white wall like 

 to the appearance of marble is moving 

 slowly eastward, whelming all vegetation 

 as it goes, some of which, able to grow 

 through the encroaching mass, persists, so 

 that all the plants now appearing on the 

 surface, so far as examined, are anchored 

 by lengthened stems or roots to the under- 

 lying older soil. The same yucca that 

 appears at E.scondida here emerges some- 

 times by green tips from a snow-white 

 drift twenty feet in height, or anon, seems 

 to crown triumphantly some lower mound. 

 The mesquite holds on, in some places a 

 desperate fight, and certain species rf h'Jtns 

 —K. aromatica and R. trllohitta, perhaps— 

 maintain a perilous existence out over the 



* The following analysis of this material has 

 been kindly furnished me by Dr. L. W. Andrews 

 of the Mallinckrodt Chemical Works, St. Louis: 



Calcium sulphate, CaSO^ 77.64 per cent. 



Water. H„0 20.55 



Calcium carbonate, CaCO, 0.95 " 



Silica and undetermined. SiO,, etc. 0.86 " 



ioo7oo 



whole region, sometimes even on the sum- 

 mits of the highest knolls. These sumacs 

 are the characteristic species of the white 

 sands. 



But let us turn north. A journey of 

 fifteen or twenty miles brings us to the 

 black wall of the lava flow. This is a fear- 

 ful region. The Mexicans call it iual imis, 

 ' bad country ' ; giant floods whose waves are 

 stone, fields and fissures, caverns, holes, pits 

 and wells, alternating with tilted slopes, 

 knife-edge culms and ridges, make a topog- 

 raphy weird, impassable, fascinating be- 

 cause so unapproachable. Yet the md 

 pais is covered with vegetation. Of course, 

 the vegetation changes, but by no means as 

 one might easily suppose. Here is no new 

 species, no variety of a species when the 

 desert is studied as a whole. The change 

 is correspondent to a change in level. The 

 lava beds are high, and they are crowned 

 with the flora of their own altitude. We 

 shall meet it on the foothills of all the 

 mountains we presently ascend. Here is 

 no alteration of soil, for the only soil is 

 that deposited by the wind, the lava itself 

 being perfectly intractable. Here are the 

 familiar mountain cedar, Junipcrus occi- 

 dentalis; cholla, sometimes twelve or fifteen 

 feet high, where, springing in some ragged 

 well-hole, it seems to peer otit above the 

 sooty walls that hem it in ; here is the 

 mountain barberry. Even the nut pine, 

 Pinus edulis, has mistaken these pitchy 

 steeps for the clayey flanks of its usual 

 mountain fastness, and now and then rivals 

 the cedar in its hold upon the jagged up- 

 turned edges of these flinty sheets. Even 

 the lava beds have not apparently affected 

 the general character of the de.sert flora. 



At the south end of these black fields, 

 however, emerge great springs. Here all 

 the plain is .saturated with salt and alkali, 

 and here is a peculiar flora conditioned by 

 this fact. The waters emerge almost from 

 the edge of the lava sheets, and tufts of 



SCIENCE. 



