102 NEW YORK STATE MUSEUM 



has remained elevated since early Paleozoic times and against which 

 earth waves of several geologic periods have broken." (In the 

 south folds through movement from south toward close of Mesozoic 

 period, in the north the folds of the Altaide system of relatively 

 recent date.) None of these earth movements affected the interior 

 and throughout the vast interior Precambrian areas of central 

 Africa the predominant strike of the foliation and folding is north- 

 south. Toward the margins, we have seen, this strike may vary 

 somewhat toward the west and east. 



As none of the Paleozoic and Mesozoic orogenic disturbances was 

 able to enter the solid crystalline massif of Africa except at the 

 margins, it follows that the predominant north-south foliation and 

 folding of the metamorphic rocks is a primary structure of Precambrian 

 age} 



Madagascar. Going east of Africa in our search for Precambrian 

 lines of trend we meet in Madagascar a large area of rocks considered 

 as of Archean age. The researches of Grandidier, Mullens, Cowan, 

 Lemoine and others have shown that this Archean region extends 

 over the central and eastern portions of the island and occupies 

 about two-thirds of the latter. It is composed of crystalline schists and 

 mostly gneiss. The Encyclopedia Britannica (v. 17, 19 10, p. 271) 

 gives the following general survey of the strikes of the Archean 

 rocks: " The general strike of the rocks is the same as that of the 

 trend of the island itself (NNE-SSW), but in its western portion 

 the strike is frequently fromNNW-SSE." Madagascar has not been 

 folded since Precambrian time and the north-south fold system of 

 the Archean rocks is therefore undoubtedly of Precambrian age. 



The Seychelles, situated far to the north-northeast of Madagascar, 

 consist of granite and, lying in the direct strike of the backbone 

 of Madagascar, undoubtedly indicate a further extension of that 

 horst in the Indian ocean. 



d Precambrian Fold System of Australia 



Australia is described by J. W. Gregory (1910, p. 943) as " essen- 

 tially the fragment of a great plateau land of Archean rocks. It con. 

 sists in the main of an Archean block or ' coign,' which still occupie s 



1 J. W. Gregory (The Rift Valley and Geology of East Africa. Seeley, Service & 

 Co. Ltd. London, 1921; Review, Amer. Jouj. Sci., 5 ser. v. 2, 1921, p. 353), 

 has explained the great Rift valley of Africa as connected with this dominant 

 north-south structure of the continent, considering the rifting as having " broken 

 through an especially stable part of the earth's crust, which consisted of a Pre- 

 paleozoic mountain chain that extended from Asia Minor to Natal." The rift 

 was first formed as a long, low arch, with the axis trending north-south; the 

 tension which caused the rupture was due to the formation of the South Atlantic 

 and Indian oceans. 



