982 Transactions of the American Institute. 



In this stage was probably thrust up the great range of the Ancles, 

 in double and parallel lines as far as Chimborazo, and there dividing 

 into three great branches. 



The mountains of Guayana %yere also at tliis time elevated and 

 perhaps some of those of the eastern coast of Brazil. From this time 

 ouAvard, through every succeeding stage of its groAvtli, these moun- 

 tain i-anges have formed the axes of oscillation for the rest of the con- 

 tinent. They have themselves undergone subsidence to receive 

 ocean deposits upon their slopes and foot hills. 



The first great period of oscillation and partial subsidence we shall 

 call the Paleozoic, extending from the silurian to the close of the 

 carboniferous eras. 



Very much the largest portion of the continent stood firm, a small 

 portion of the middle, viz., Bolivia, part of Paraguay and part of 

 Brazil. Exactly how large these areas were we do not know. "We 

 are dealing with fragmentary history, and cannot speak with preci- 

 sion. They may have been much larger. than represented upon the 

 Paleozoic map. The next great period is the Mesozoic. In this 

 the axes of oscillation were changed. The Guayanas, much of Bra- 

 zil, the entire range of the Andes, and many local poihts in Buenos 

 Ayres stood firm, while the great plains of the continent subsided 

 beneath the ocean and received deposits from abrasions and detritus 

 of the older portions. We see Brazil retaining its present contour, 

 but much abbreviated of its territoiy. 



During this stage of the growth of South America, it presented a 

 long nai-row rim of land on the west, connected with the large 

 islands of Brazil. There was an archipelago of islands in the north, 

 much like the West Indies, and a smaller group in the south. 



My third great division of the growth of this continent is the 

 dilurial. This is confined mostly to the valleys of the great rivers^ 

 and the coast line of Brazil, north of the Amazon, and Cape St. 

 Rogue. The coast of Guayana, the delta of the Oi-inoco, the 

 Lakes Maracaibo and Titicucu, and a narrow shoreline of the Pacific. 

 It is but a small fragment of the continent, but of great importance 

 in studying the laws which have controlled the changes this conti- 

 Dent has undergone, and the agencies which have produced them. 



A glance at a well executed physical atlas will sliow that this last 

 addition to the continent has been made by causes now at work. 

 Atmospheric and other agencies cause decomposition of rock masses 

 and all land elevated above the sea level. The rains of heaven cause 



