128 HATCHER — OLIGOCENE AND MIOCENE DEPOSITS. [April 3, 



beds appears to the writer not only to be in harmony with all the 

 observed facts, but moreover the conditions which it presupposes 

 are paralleled by existing conditions in other parts of the earth's 

 surface. 



The following description of the conditions at present prevailing 

 about the sources of the Parana and Paraguay Rivers in central 

 South America has been furnished me by Mr. H. H. Smith, 

 who has spent several years in that region and has had exceptional 

 advantages for studying the physical conditions that obtain about 

 the headwaters of these streams and their tributaries. He says : 



*' Ascending the River Paraguay from Asuncion, the river hugs 

 the higher lands of the eastern or Paraguay side or is separated from 

 them by strips of alluvium. On the western or Chaco side the 

 ground is always low and flat, hardly above reach of the annual 

 freshets and proportionally a little lower toward the north. 

 During the rains water covers large spaces of these flatlands, but 

 it does not come from the river and is gradually drained away 

 after the rains cease. Above the mouths of the A^ermejo the 

 Chaco bank is at first covered with low forest ; farther north 

 great areas have a scattered growth of Caranda palms with grass 

 beneath, but with no other vegetation. The Chaco plains extend 

 far inland to the table-land of Bolivia, which is said to fall abruptly 

 to the plain. 



*^ At latitude 21° 26' 40'' S. the river flows through a narrow pass, 

 the Fecho dos Morros, between two rocky hills. The hill on the 

 eastern side is connected by high ground with the Brazilian table- 

 land. That on the western side appears from the river to form one 

 of a number of isolated hills which rise from the Chaco plain. It 

 may be, however, that there is rocky ground extending westward to 

 the Bolivian table-land, and perhaps connected with the Corumba 

 hills. This region, however, is practically unexplored, and nothing 

 definite can be said about it. If there is a connection with the 

 Bolivian highland, the basin of the upper Paraguay is completely 

 enclosed like a lake, with only the narrow outlet at the Fecho dos 

 Morros. If the hill on the western side is isolated, it is probably 

 one of a chain which extends inland and imperfectly closes the 

 Paraguay basin on this side. 



*' Above the Fecho dos Morros the character of the vegetation 

 changes ; the Caranda palms disappear ; there is left only open 

 grassland, with lines of bushes here and there and often a thin 



