SERILAND 
129 
The geolog}^ of Seriland is worthy of study. The prevailing 
rocks of the principal ranges are rather ancient (probably Meso- 
zoic or early Tertiary) lava sheets with associated tuff's and brec- 
cias, while in several localities, notably the western foot-slopes of 
Sierra Seri, there are large areas of still more ancient granite, 
often slightly schistose and intersected with dikes and veins. It 
is tlie current belief in Sonora (a belief based partly on the use 
of rare minerals as face-paint among the Seri) that rich deposits 
of ores and precious metals exist in Seriland, and certain por- 
tions of the area examined certainly appear worth prospecting ; 
but no rich deposits were found, and most of the rocks examined 
are unpromising. The dominant geologic feature of the territory 
is that reflected in the topography — the abrupt transition from 
rugged mountain to smooth peneplain of similar rocks with a 
veneer of fragmental debris. Generally this debris is unconsoli- 
dated and fresh-looking, though sometimes it is cemented by 
siliceous or ferruginous matter, and toward the eastern side of 
Desierto Encinas even the superficial portions of the alluvium 
are somewhat indurated, as if by calcareous infiltration, into a 
mass known as caliche in western Mexico (the tepitate of eastern 
INIexico). No deposits postdating the extravasation of the lavas 
and the outlining of the mountain ranges were seen save the 
shell-charged sands of Encinas desert; these deposits and the 
shelf skirting Tassne island on north and east suggest relatively 
recent uplifting, while the configuration of shores, especially in 
Estrecho Infiernillo, demonstrates relatively recent subsidence, 
so that to one of us, at least, the combined records indicate local 
warping. To some extent in Seriland, as decidedly in contigu- 
ous Papagueria, the divides are migrating northeastwardly, and 
this widesi)read characteristic suggests a relatively recent tilting 
of the land southwestward, whereby the feeble streams- flowing 
with the increasing sloi)e are stimulated while those flowing 
against it are paralyzed. 
The meager flora of Seriland is peculiar. The conspicuous 
forms are cacti, comprising the monstrous saguesa (a Cereus 
related to f/Ujaideas but still larger) and wide-branching pita- 
liaya (Cereus Ihurheri) on the foot-slopes, with the cina (Cereus 
sehoUil) and cholla (a cylindropuntia) at lower levels and the 
water-bearing bisnaga ( Kchinocarlus) here and there on thenniin- 
land, though few and far between on the island. The ghostly 
okatillo (/'ba7/n>m .s/>/(j/tdr/ix) is fairly abundant, and there are 
occasional yuccas and a variety of the more slender agaves. The 
