THE SOIL 167 



the sub-Andean chains, and marks the limit of the 

 area with sheets of underground water. In the north 

 of the Pampean region, between the Sierra de Cordoba 

 and the Parana, the loose continental formations are 

 more than 2,000 feet thick at Bellville, and more than 

 3,500 feet north-west of Santa Fe (fodder farms of San 

 Cristobal and El Tostado). At Buenos Aires the granite 

 has been found 985 feet below the surface. 



The Pampean formation consists almost entirely 

 of loose deposits, sand and clays of various sorts. 

 There is no gravel. ^ Even in the vicinity of the sierras 

 the beds of gravel, with round or angular pebbles, are 

 almost always covered by clay, and are exposed only 

 in the banks of the streams. Olascoaga mentions 

 the surprise of the gauchos of General Roca's army when 

 they found Patagonian pebbles on the ground during 

 their stay at Choele Choel on the Colorado, in the course 

 of the compaign on the Rio Negro. Officers and 

 soldiers dismounted to pick them up. Sand and clay 

 form a thick bed of continental alluvia. The Tertiary 

 maritime transgressions, which have left their mark 

 in the clays and limestones of the left bank of the 

 lower Parana, and the layers of shells at San Pedro 

 on the right bank, never penetrated far into the interior 

 of the Pampean region, and one finds no trace of them 

 when one leaves the coast or the river. 



The source of the elements which compose the 

 Pampean alluvia is very uncertain. Their composition 

 does not clearly show their origin. The clays are com- 

 paratively rich in calcareous matter, which seems 

 to indicate that they do not come from tropical America 

 or the upper basin of the Parana. Wright and Fenner 

 insist upon the high proportion of siliceous glass of 

 volcanic origin which they contain, which points to 



• Roth claims to have found gravel in the San Nicolas barranca 

 on the Parand. I have myself found small rounded flints in the clay 

 of the Chaco at Tartagal. But these deposits probably come from 

 the left bank of the Parana, where the beds of river gravel are con- 

 siderable. 



