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INSTITUTE OF SOCIAL ANTHROPOLOGY — PUBLICATION NO. 10 



the south, by the Franciscan Missions of Guarayos; 

 on the east, by the Rio San Martin; and on the 

 west, by the Rio Grande and Rio Mamor6. Within 

 this extensive area the Siriono have lived and 

 wandered in isolated pockets since the first Euro- 

 pean contact with them in 1693. 



Until the 1930's, a great many Siriono were 

 living in the island forests of the Mojos plains east 

 of Trinidad and between the Rio Grande and Rio 

 Ph-dy, but now most of these have become ac- 

 culturated and are living under conditions of al- 

 most forced labor on cattle ranches, farms, schools, 

 and missions near Trinidad, Magdalena, Baures, 

 El Carmen, Guarayos, and Santa Cruz. Actually, 

 almost the only unacculturated Siriono extant 

 today are those occupying the forest country 

 southeast of the village of El Carmen. Here, 

 east of the banks of the upper Rio Blanco, is lo- 

 cated a range of hills, locally known as the Cerro 

 Blanco, near which wander a few groups of Siriono, 

 who have as yet been unmolested by white contact. 

 There may also still be some living between the 

 Rio Grande and Rio Pirdy, but these have not 

 been seen by me. 



The region occupied by the Siriono is character- 

 ized by a tropical climate with two seasons, the 

 wet and the dry. The former lasts from November 

 to May; the latter from May to November. The 

 annual mean temperature (no records available) 

 runs around 73° F., with extremes of 50° F. during 

 the cold south winds from Tierra del Fuego and 

 110° F. during the heat of the average day. Dur- 

 ing the rainy season the climate is very hot and 

 moist, with rains on the average of every other day ; 

 during the dry season the extreme heat of the day 

 is tempered by cooler nights and occasional cold 

 wind stoi-ms from the south. These "sures," as 

 they are called by the Spanish-speaking natives 

 of the region, are usually accompanied by rain 

 and a very sudden drop in temperature. They 

 generally last about 4 days and occur at average 

 intervals of 15 days during April, May, and June. 

 The prevailing winds, however, are from the north. 

 The average rainfall is about 100 inches per year. 



Geographically speaking, the Siriono country is 

 situated in the eastern part of the vast plain, 

 partly forested and partly pampa, lying between 

 the Andes on the west and the Mato Grosso 

 Plateau on the east. From south to north, this 

 plain extends from the hill country north of the 

 Gran Chaco to the low unexplored hills of Brazil 



which lie just north of the Rio Guapor6. Within 

 this area, from the Rio Blanco west to the Rio 

 Mamore, are located the extensive llanos of 

 Mojos dotted with the island forests once occu- 

 pied by the Siriono. East of the Rio Blanco, 

 however, between the Rio Guapor6 on the north 

 and the Franciscan Missions of Guarayos on the 

 south, is a vast and dense forest plain which rims 

 for himdreds of mUes, and within which the few 

 extant Siriono still wander today. This plain 

 contains occasional low ranges of hills, which are 

 part of the same chain that runs into Brazil on 

 the north and into the Chiquitos region of Bolivia 

 on the south. 



Except for the above-mentioned lulls, the area 

 generally is flat and only about 500 feet above sea 

 level. Both the pampas and the forests are 

 characterized by alturas — high lands that do not 

 flood during the rainy season — -and bajuras — low 

 lands that do flood in the rainy season. The 

 alturas are characterized by a resistant cappuig of 

 partially decomposed lava, containing a top soil 

 of coarse sand with occasional outcroppings of 

 igneous rock. In elevation they lie some 75 feet 

 above the bajuras, which are made up of a heavy 

 clayey top soil and which are flooded during most 

 of the rainy season. The alturas of the forest are 

 considered to be the richest agricultural lands, 

 while the bajuras of the pampa, since water 

 stands in many of them the year around, are 

 suitable for little more than grazing. 



The outstanding watershed features of the re- 

 gion are its numerous lakes and rivers. Of the 

 former there are some 20 large ones in the Siriono 

 country known to me, but which have not been 

 named as yet. Around all of these lakes are ex- 

 tensive flood lands, and stenuning from each are 

 brooks or arroyos which drain into other lakes or 

 into the principal rivers of the area, the Rio San 

 Martin, the Rio San Joaquin, the Rio Negro, the 

 Rio Blanco, Rio Itonama (San Miguel or San 

 Pablo), and the Rio Machupo. All of these 

 rivers flow mto the Guapore (Itenez) before it 

 joins the Alamore (Madeira) in its route to the 

 Amazon. The southwestern part of the area 

 is drained by the Rio Pirdy and Rio Grande, which 

 also flow into the Mamore. Although the rivers 

 are numerous and of good size, the area in general 

 is poorly drained; from the air during the rainy 

 season it has somewhat the api3earance of a huge 

 swamp within which there are islands of high 



