48 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



A different result follows when the grass and loess are intimately 

 mingled. Esparto is a grass which sends up blades from root-stocks 

 below the surface. The blades grow close together, catch more or 

 less dust between the stems, and become partly buried to a depth 

 depending on local conditions, perhaps 10 or 15 cm. or more. .When 

 esparto burns, the loess about the grass stems is calcined down to 

 and around the roots below the surface of the plain. The writer 

 observed an instance in the delta of the Rio Colorado. A bright- 

 red spot in the greenish-brown plain attracted attention. On riding 

 to it, it was found to be an area a hundred meters more or less in 

 diameter, where the esparto, which grew in tufts all about, had re- 

 cently been burnt. The stems and roots were burned out, leaving a 

 spongy mass in which a horse sank to his fetlocks. It was composed 

 of thorougldy calcined earth, varying in color from pink to brick- 

 red, in part scoriaceous. Coherent masses 10 cm. or more in diameter 

 could be picked up, but they were penetrated in every direction by 

 hollows formerly filled by the stems and roots, and were very fragile. 

 They carried impressions of grass stems, bits of carbonized grass, 

 etc., and in these respects corresponded with specimens obtained from 

 the Pampean by Doctor Ameghino and described by him. 



These observations lead the writer to give weight to the views 

 of those early observers, who attributed the tierra cocida of the 

 Pampean terrane to the burning of grasses. 



There is notliing, however, to connect the burnt earths of the 

 Pampean with man, so far as the occurrences were observed by the 

 writer. Any fire whatever, whether originating in spontaneous 

 combustion, in lightning, or in other natural conditions, independent 

 of man, would have the effect of burning the earth under favorable 

 conditions. In order to prove that man maintained a fire which 

 burned a particular mass of tierra cocida it would be necessary to 

 bring independent evidence of his handiwork. Two classes of facts 

 have been cited to demonstrate his agency : The presence of supposed 

 artifacts and the arrangement of a mass of burnt clay; cliief among 

 the former are split, broken, or scratched fragments of bone, and 

 it appears to the writer that these may be referred, with greater 

 probability, to weathering, biting, gnawing, and accidents incident 

 to the wanderings of bones, as strata were eroded and redeposited. 

 Certainly the proofs of man's agency should be uncontrovertible and 

 the possibility of explanation by other than human action should be 

 positively excluded, before the conclusion that he intentionally or 

 incidentally burned the earth can be accepted. 



This critical test should be met equally by occurrences where the 

 mass of burnt earth and its relations to the surrounding unburnt 

 loess suggest that man built and maintained a fire over the spot. 



