IV. TIERRA COCIDA; SCORL^ 



By Bailpjy Willis 



Tierra cocida, or burnt earth, occurs in the Pampean terrane at 

 various horizons, as shown by the researches of Amegliino, Roth, and 

 others. The material resembles brick, or in places scoria, and 

 occurs commonly in the form of small pebbles. Occasionally larger 

 masses have been found. Ameghino has described the tierra cocida 

 with accuracy and in great detail. Through his courtesy the writer 

 has been able to verify the descriptions by examination of the original 

 specimens, which form part of the collections of the Museo Nacional 

 at Buenos Aires. 



The burnt earth varies in character and color from brown or fawn- 

 colored loess, through various tints of pink or brick to dark iridescent 

 or black scoria. Some specimens are of close texture, like a fine- 

 grained brick, but the scoriaceous specimens are very porous. It 

 occasionally contains impressions of strongly ribbed grasses, and in 

 rare instances includes bits of carbonized grass stems, little bones, 

 and other things of organic origin. There are also specimens which 

 are distinguished by a dark color and slaggy appearance. These 

 are heavy, though scoriaceous, resemble volcanic scoria, and have 

 rbeen described as such. They have been found mainly on the coast 

 of the Province of Buenos Aires, where volcanic scoria may occur 

 as wash brought along the coast from tuffs in the territory of Rio 

 Negro. It is important in considering their character and origin 

 to distinguish between those which are washed up on the beach 

 and those which occur in the Pampean terrane, as will appear 

 presently. 



The writer collected specimens of the so-called tierra cocida in 

 company with Doctor Ameghino and Doctor Hrdlicka on the eastern 

 coast, with Roth at Saladillo near Rosario, and alone in the delta 

 of the Rio Colorado south of Bahia Blanca. The last-mentioned 

 occurrence is modern, while the others pertain to the Pampean ter- 

 rane. Brief descriptions of the observations made in the course of 

 this work will be found in the following pages. 



On visiting Saladillo with Doctor Roth, a section of the dark-brown 

 loess loam, which Roth classed as Upper Pampean, was found 



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