Apeil 3, 1896.] 



SCIENCE. 



495 



torrential debris, fine at the lower levels, 

 coarser toward the bounding foot-hills and 

 ranges, though it is remarkable, and indeed 

 paradoxical, that they consist in large part 

 of the planed edges of hard rock strata such 

 as form the adjacent mountaias; the sur- 

 face of the plain, whether built or carved, 

 being sparsely dotted with trees and shrubs 

 of sub-desert habit. Toward the coast the 

 plains lie but little above and in some cases 

 apparently below sea-level, and are com- 

 posed of marine sediments, sometimes 

 abundantly charged with recent shells ; 

 when the surface is usually a succession 

 of playas and sand dunes. 



Seriland is an exceptionally mountainous 

 portion of the great westward- sloping plain, 

 lying near the line along which it dips be- 

 neath the waters of the gulf ; indeed a part 

 of this staunch little domiuion lies beyond 

 the general coast line and is separated from 

 the mainland by a narrow strait, itself the 

 precise homologue of the upland intermon- 

 tane valleys save that it is occupied by tide 

 water and faintly sculptured by waves and 

 tidal currents. The main insular portion 

 of the territory is Tiburon Island, about 

 500 square miles in area ; the continental 

 portion is some 2500 square miles in area; 

 and a few small islands adjacent to Tiburon 

 and the Sonoran coast belong to the same 

 natural district, and are held by the Seri 

 Indians. Tiburon Islaad comprises half a 

 dozen ranges, major and minor, the higher 

 peaks rising from 3000 to 4000 feet above 

 tide; in its principal interior valley there is a 

 feeble stream, gathering among the higher 

 peaks and wasting within a few miles, be- 

 sides some half dozen tinajas and springlets. 

 Sonoran Seriland is also mountainous, the 

 culmiaating peak rising about 5000 feet 

 above tide, and contains a feeble permanent 

 spring and two or three water holes in 

 which the water is brackish. Of the entire 

 area south of Gila river and west of the 

 Sierra, about four-fifths may be classed as 



plain, one-fifth as mountains; but in Seri 

 land more than two-fifths and probably 

 three-fifths must be classed as mountains, 

 leaving only a moderate fraction to be 

 classed as plain. This mountainous tract 

 is separated from Papagueria by a broad 

 waterless zone of playas and sand dunes, 

 abounding in partially fossilized shells. 



It is to this desert barrier, 20 to 40 miles 

 across, that the isolation, and appar- 

 ently many of the characteristics, of the 

 Seri Indians are due; for it is a natural 

 boundary, one of the most trenchant and 

 effective on the Continent, practically im- 

 passable without special training, and so- 

 conditioned as to be easily defended along; 

 the inner margin in case of invasion. 



When the mountains and intermontane 

 plains of Papagueria and Seriland are ex- 

 amined in detail, certain peculiarities ap- 

 pear : As already observed, the mountains 

 are notable for ruggedness and the plains 

 for flatness nearly or quite to the mountain 

 bases ; again, the parallel ranges are found 

 to be occasionally united by cross bars, so 

 that a common form of mountain plan may 

 be likened to the letter H ; still further, it is 

 found that the larger arroyas and rivers 

 seldom follow the axes of the valleys, but 

 usually flow athwart them and frequently 

 traverse the bounding ranges in narrow 

 gorges opening toward the gulf, while many 

 southward-flowing streams head on the 

 northern sides of the cross-bar ranges 

 through which they pass in youthful can- 

 yons. On a ssembling these peculiarities, they 

 are found to point toward two successive 

 sets of geologic conditions: The distribu- 

 tion of the minor ranges with their trans- 

 verse connections, coupled with the fact 

 that a large part of the area of the inter- 

 montane plains is planed, indicates that the 

 region was formely a plateau which main- 

 tained its altitude and attitude until the 

 feeble sub-desert streams degraded the 

 greater part of the mass, leaving onlj' the 



