I 



TRANSACTIONS OF SECTION E. 929 



of material thus taken out near its top. At the bottom of the excavation I found 

 several frag^ments of quartz rock, like that on the southern slopes of the Sierra 

 Ventana. In all the dunes composed of pure sand I found, by digging four 

 inches below their surface, on their sides or summits, that the sand was quite wet. 

 Such was the case during our stay, although a very dry season. Numberless 

 little lagoons, from 50 to 150 feet in diameter, with bottoms of soft mud, are 

 scattered among them, around the margins of which grow rushes, weeds, and 

 bunches of the exquisitely beautiful pampa-grass, the Gtjnerium argent ium. 

 Often, when the ponds were nearly dry, the soft, silky flowers of the pampa-grass 

 had covered their muddy bottoms with a white mantle. Numerous aquatic birds 

 are to be seen swimming in the shallow water of the open ones. Sporting with 

 each other are nutrias (the South American otter, the Myapotamus Coi/pus), ducks, 

 geese, black-necked swans, water-hens, and rose-coloured spoonbills, all so tame 

 that I could sit on horseback within 20 feet of them without disturbing the 

 amusements. I have counted fourteen otters in a small lagoon ; and, from the 

 apparent fomiliarity with which they rubbed noses with the ducks, they were as 

 much a part of the family as any of the feathered tribe. I never molest them. 

 It would be a pity to break in upon their Arcadia.' 



I have lingered among the Ventana Mountains and in their vicinity, as they 

 were once lofty islands which played an important rd/e in arresting and protecting 

 the Pampean mud. 



EasterJi Boundary of the Basin. — Cuvaba, at the head of the Paraguay River, is, 

 according to numerous observations of Clauss, only 660 feet above sea-level. The 

 valleys around it are bounded by vertical cliff's of red sandstone overlying argilla- 

 ceous shales, which easily disintegrate. The Matto Grosso highlands, south of 

 Cuyaba, as far as Paraguay, are practically unexplored ; but I have no doubt they 

 are of the same formation of sandstone and shales resting on metamorphic rock. 



The Apa River, which is the northern boundary of Paraguay, drains a limestone 

 district. Bourgade says 'the main framework of Paraguay is a dark-red sand- 

 stone, but basaltic formations may be seen in many parts. Immense areas are 

 covered to a considerable depth by u fertile red earth representing the decomposi- 

 tion of the sandstone hills.' 



From Asuncion, the capital of Paraguay, south-east to the Apipe rapids of the 

 river Parana, the Cordillera of Caa-guazu "throws off a range of hills which over- 

 look a great triangular space at the south-west corner of Paraguay, slightly 

 elevated above the sea, and consisting of low, sandy ground and morasses, at times 

 flooded by the Paraguay River. This district, united to that of the Ybara lagoon, 

 in Northern Corrientes, was probably the delta of the Parana when it emptied into 

 the ancient Pampean sea. The river is charged with but little silt in comparison 

 to its much smaller affluent, the Paraguay ; but, in flood, it carries a volume of 

 water, said to be ten times that of the latter stream, and its width, along the 

 northern sandstone border of Corrientes, is from three to nine miles. The alluvium, 

 from the immense area of Brazil which it drains, is arrested by the rapids, reefs 

 and falls of its middle course, where it violently tears a deep channel through huge 

 beds of red sandstone, to afterwards unite its yellowish waters with those of the 

 muddy Paraguay. 



Lying between the rivers Parana and Uruguay is the Argentine Mesopotamia, 

 the provinces of Corrientes and Entre Rios, covered with modern alluvium. The 

 former is gently undulating, and is half drowned in lagoons, the largest being the 

 famous Ybara. The south and south-western part of Entre Rios is composed 

 extensively of argillaceous earth, and the whole State is traversed by ridges of low 

 hills running nearly north and south, the main ones never exceeding an altitude 

 of 650 feet above sea-level. The framework of the province is of sandstone, 

 covered in some places by shell limestone, and sometimes by granular limestone. The 

 north-eastern part is sandy, with numerous hillocks of siliceous gravel. The exposed 

 sandstone, on the river Gualeguay, extends north almost to the Ybara lagoon. On 

 the left bank of the river Parana, just south of its junction with the Paraguay, 

 is the town of Corrientes, built on a red sandstone bluff. The same stone shows 

 for thirty miles down stream, where it disappears, and thence for 240 miles the 



1898. 3 o 



