42 THE SERI INDIANS [eth.ans.17 



inner margin of tlie shelf is a seacliff, usually 30 to 50 feet liigb, of 

 which the lower half is conunoiily granite and the upper half unconsoli- 

 dated and recent-looking mechanical debris collected by sheettlood 

 erosion. Sometimes the granite of the subterrane is replaced by vol- 

 canics; sometimes ancient and firnily cemented talus deposits separate 

 the superficial mantle from the subterrane, as shown in the lower part 

 of plate V; sometimes the line of sheettlood planation passes below 

 tide level, when the waves beat against the unconsolidated deposits in 

 a deep embayment; sometimes the sharply deli ued planation surface 

 ends abruptly at the sides of subranges or buttes shooting upward in 

 the abrupt slopes characteristic of the sierra proper; yet this 10-mile 

 stretch of coast is a nearly continuous revelation of tlie structure of 

 sheetilood-carved plains and of modern marine transgression. The 

 debris of the combined processes forms an abundant and varied assort- 

 ment of bowlders, col)bles, and pebbles, whence the inhabitants readily 

 derive their simple implements without need for studied forethought 

 or manual cunning. 



The long sand-spit terminating in Punta Miguel ajid the shorter one 

 terminating in Punta Arena are the product of geologically recent 

 wave building, and consist of irregular series of V-bars, backed by 

 lagoon-like basins and enclosing considerable bodies of brine in the 

 central portions; and the bars and basins become successively higher 

 outward, in such wise as to attest the secular subsidence of this coast. 

 Several jacales are located on the higher portion of the southern sand- 

 spit, midway between Punta Granita and Puuta Miguel, while foot- 

 l)aths traverse the Hat and skirt the coast. Toward the terminal por- 

 tion of the spit the sand is blown into hummocks, held by clumps ot 

 salt enduring and sand-proof shrubbery; but there are no rancherias 

 here, despite the fact that it is a natural point of embarkation — doubt- 

 less because no Seri structure could withstand the sand drifting gales 

 and storm inundations of this exposed spot. The more protected 

 lagoons behind the outer bars harbor abundant waterfowl, withiu 

 bowshot of shrub-clumps and dunes well adapted to the concealment 

 of hunters, while the mudflats open to the tide abound in clams and 

 other edible things. The features of the Punta Miguel sand-spit are 

 repeated with variations along the eastern shore of El Infiernillo; and 

 Seri jacales, evidently designed for temporary occupancy, occur here 

 and there, usually on higher banks above reach of the severer storms. 



3. Tiburon island itself is apparently the chosen home of the Seri — 

 a habitat to which the mainland tract is at once a dependency, an alter- 

 native refuge, and a circumvallation. Its dominant range. Sierra Kun- 

 kaak, mates Sierra Seri in its essential features, though the rocks are 

 for the greater part ordinarily obdurale eruptives rather than excep- 

 tionally obdurate granites, as in the mainland sierra; accordingly the 

 range is somewhat lower and broader, while the sheettlood sculpture, 

 with its sharp transition into precipitous cliffs, is somewhat less trench- 



