THE PAMPEAN PLAIN. TRES ARROYES (BUENOS AIRES PRAIRIE 

 BETWEEN THE SIERRA DE TANDIL AND THE SIERRA DE LA VENTANA). 



Zone of wheat and oats on large scale. The Pampa is a tableland here (400 feet above sea-level), 

 with clay overlying the limestone of the Tosca. The valleys are well marked. 



Photograph by the Author. 



THE PAMPEAN PLAIN. TO AY, ON THE CENTRAL PAMPA (^90 FEET). 



The tableland, with a strong framework, of limestone Tosca, is cut across by well-marked dry 

 valleys which sink lower toward the east. At the edges of the valleys the sand is the prey of 

 the winds. Here we are near the limit of the wheat belt. Photograph by the Author. 

 PLATE XV. To face p. 166. 



