CONTINENTAL DISPLACEMENT SCHUCHERT 265 



time, and accordingly are of so vast an age and so little known that 

 any advocate can read into them what he will. At the discussion 

 before the British Association in 1922, Coleman pointed out that no 

 dependence can be placed on them, since " the Archean is a universal 

 formation," meaning that Ave have as yet not enough precise knowl- 

 edge of these exceedingly ancient times to make long-range corre- 

 lations. 



According to Lake," " In the Hebrides and northern Scotland, 

 Wegener says, the strike of the ancient gneiss is from northeast to 

 southwest ; in Labrador it is from east to west." However, " the 

 Survey Memoir on the Northwest Highlands gives the prevalent 

 trend as west-northwest-east-southeast, or east-west." 



THE FRANCISCAN GEOSYNCLINB AND AFRICAN GEOLOGY 



We will now take up a structural element in the eastern part of 

 South America that is unknown to Wegener, because it has never 

 been presented in generalized form. In its revelation of how little 

 the geology of Brazil is related to that of Africa, it deals, however, 

 a crushing blow to the displacement hypothesis. 



Some years ago, in a study of the seaways of South America, the 

 writer was surprised to find that there is a slightly northeast-south- 

 west trending geosyncline in eastern Brazil. This trough he has 

 called the Franciscan geosyncline, taking the name from the large 

 San Francisco River that lies in a great length of it. Evans's map of 

 the tectonic lines of South America, reproduced by Wegener (p. 50), 

 correctly shows the trend-lines for this trough, but at the northeast 

 he has southeast-northwest strikes, which must be of pre-Cambrian 

 foldings; accordingly, the trough pas^sed over this old ground and 

 grain. 



This Franciscan geosyncline of eastern Brazil is a long and nar- 

 row marine trough present at least since the early Silurian. It was 

 not folded into mountains until middle Permian time, and apparently 

 then on the west and northwest. Later on, the area of the geosyncline 

 was also invaded by fresh- water strata of late Triassic age, and 

 finally, during latest Triassic and earliest Jurassic time, an area at 

 least 300,000 square miles in extent between the Amazon, Parana, 

 and La Plata Rivers was covered by plateau lavas averaging about 

 1,000 feet in thickness. These are overlain by fresh-water sandstones 

 thought to be of Cretaceous age. None of these post-Permian forma- 

 tions are folded, though they are more or less normally faulted. 



The Paleozoic sediments are essentially sandstones and shales hav- 

 ing a united thickness of less than G.OOO feet, though there may also 

 be present strata older than the Silurian. The Silurian and Devonian 

 are marine deposits, about 2,000 feet thick, while those of the 



i=Op. cit., p. 343. 



