THE LAVA FIELD OF THE PARANA BASIN 71 



volume is about 50,000 cubic miles. This is of the order of volume 

 of a great mountain range. It is certain that the basalt once 

 covered a much greater area, from which it has been removed by 

 erosion during all the latter Mesozoic and Cenozoic. The entire 

 region of sedimentary rocks in southern Brazil, east of the present 

 limits of the flows, is cut by extraordinary numbers of sills and dikes 

 of diabase. They are less numerous in Rio Grande do Sul, but in 

 the other southern states of Brazil one would scarcely ever be out 

 of sight of one or more intrusives if the country was not densely 

 forested. The sedimentary rocks cut by diabases cover an area 

 of about 75,000 square miles (nearly 200,000 square kilometers). 

 Combining the area of present flows with the area along its eastern 

 margin which probably was once covered, we arrive at the total of 

 more than 375,000 square miles (or about 1,000,000 square kilo- 

 meters) . 



Even this may be far short of the total original area. At no 

 place did the writer succeed in reaching the limit of the diabasic 

 intrusives. He found them in the basement complex of southeastern 

 Brazil, also cutting sedimentary rocks as far west as the Gran 

 Chaco in the vicinity of Asuncion, Paraguay, and Walther found 

 them as far south as Montevideo. The writer found them in the 

 southern part of Amazonia. A still greater extension is problem- 

 atical. Nevertheless, in Piauhy and Maranhao, states of northern 

 Brazil, sediments referred to the Permian and Triassic are cut by 

 diabases, and amygdaloidal sheets are intercalated with the youngest 

 sandstones of the " Permo-Trias " series. Great intrusives of 

 diabase which cut sediments as late as the marine Upper Pennsyl- 

 vanian and the overlying Red Beds, and antedating sediments 

 referred doubtfully to the mid-Tertiary on both sides of the lower 

 Amazon geosyncHne, likewise the great masses of trappean rocks 

 forming a part of the extensive mountainous area on the frontiers of 

 Brazil, Guiana, and Venezuela, may be of the same age as the 

 flows and intrusives of the Parana Basin. There are heavy flows 

 of basalt interbedded with the red continental sandstones of north- 

 western Argentina, but these the Argentine geologists, somewhat 

 doubtfully perhaps, consider Cretaceous. There are also diabase 

 dikes in the Falkland Islands. 



