WILLIS] TIEERA COCIDA; SCORLE. 47 



red tierra cocida, and distinct masses of heavy black scoriae ranging up 

 to 8 or 10 cm. in diameter. The latter resemble an opaque slag, im- 

 perfectly fused, and cooled from a pasty state into irregular individual 

 lumps. Each specimen of the four that were gathered was complete 

 in itself, not a fragment of a larger mass. They occurred imbedded in 

 homogeneous loess, in which they were in place, like pebbles in shale. 

 Judging from their general appearance that they might be of volcanic 

 origin, the writer carefully noted that they were not washed up on 

 the beach and buried in a recent deposit of the loess. They occurred 

 in the undisturbed Pampean, and if they were volcanic would dem- 

 onstrate that scoria of appropriate character had existed in a place 

 from wliich these masses could have reached their present position. 

 According to Mr. Cross, whose opinion is quoted below, they are 

 probably not volcanic. This inference therefore fails but it is still 

 possible that scoriae of volcanic origin should be found in this locality, 

 as they occur along the same coast farther south, and tuffs and 

 basalts cover a large area in the territory of Rio Negro near the 

 Colonia Valcheta and elsewhere, as observed by Senor Moreno in 

 1873-74. Masses so derived and washed along the coast would 

 occur only in modern formations, for the present coast is modern. 

 During the Pampean epoch the shore was farther east and the 

 coastal wash could not have reached this position. Hence the 

 importance, above referred to, of distinguishing the precise relations 

 in which any such supposed, volcanic scoria occurs. 



Mr. Whitman Cross, of the United States Geological Survey, reports 

 as follows on the specimens collected from this locahty near Miramar 

 and submitted to him: 



''Among the explanations of the occurrence of 'tierra cocida' in 

 the Pampean is one advanced by £arly writers, as quoted by Ame- 

 ghino, to the effect that burning grasses had calcined and fused the 

 loess. To investigate this suggestion the writer burned several 

 heads of the great Pampas grass or cortadera, both growing and dead. 

 The growing tussocks consist in the winter season of a large, almost 

 solid head, which is green, and of dried leaves. The latter burn 

 readily down to the green head, but the fire does not reach the ground. 

 When cortadera is dead the head also burns and the fire lasts a num- 

 ber of hours. A large plant, fired at 5 o'clock of an afternoon, was 

 still a glowing mass at 7 the next morning. The effect on the under- 

 lying earth was, however, shght. The loess was reddened to a depth 

 of 10 milhmeters, more or less. It was not calcined to a brickUke or 

 scoriaceous mass. The ground was dry at the time. The fire had 

 been intense and had burned 14 hours. It had, however, been prac- 

 tically on the surface, and the writer infers that superficial heat does 

 not notably calcine loess." 



