DIASTROPHISM AND THE FORMATIVE PROCESSES 329 



were affected by folding which took place between the Silurian and 

 Devonian/ 



Over considerable areas in southeastern Brazil horizontal beds 

 of Devonian age rest unconformably upon folded and metamorphic 

 rocks for the most part of probable pre-Cambrian age, but possibly 

 including some strata representing the Cambrian or Lower Silurian.^ 

 This is the most conspicuous period of deformation to which the 

 eastern half of the continent of South America has been subjected 

 since Archean times. It resulted in a great chain of mountains, 

 of which the present Serra do Espinhago, or Backbone Range of 

 Brazil, represents the roots. The time of the crumpling and fault- 

 ing has not yet been closely determined, and this cannot yet be 

 classed as a Siluride movement, though Hauthal believes that 

 the Sierra de la Ventana, in which he found evidence of a Siluride 

 movement, are related in origin to the BraziHan Highlands. 



In New South Wales, according to Siissmilch, the Silurian 

 period was brought to a close after a long period of sedimentation, 

 by a pronounced deformative movement which folded and elevated 

 the Silurian strata to such an extent that much of the country was 

 raised above sea-level. Incomplete knowledge of the nature and 

 distribution of the succeeding Devonian sediments makes it 

 impossible to form any definite opinion as to the extent of this 

 movement. 3 But farther north, in the Narrigundah Gold Field of 

 Queensland, Devonian strata are again found resting horizontally 

 upon folded Silurian beds."* 



Like the closing stage of the Ordovician, the end of the Silurian 

 period was a time of rather general crustal disturbance which 

 reached extreme intensity in certain regions. Present knowledge 

 is not adequate, and correlations are not sufficiently exact, to deter- 

 mine how nearly simultaneously the disturbances appeared in the 



iR. Hauthal, "Excursion a la Sierra de la Ventana," Publicaciones de la Uni- 

 versidad de La Plata, 1901, pp. 30. 



2 Hartt, cited by Suess, op. cit., I, 508. J. C. Branner, Geologia Elementar, Rio de 

 Janeiro (1906), p. 217. 



3 C. A. Sussmilch, An Introduction to the Geology of New South Wales (1911), p. Zd>- 

 iH. I. Jensen, "The Building of Eastern Australia," Roy. Soc. Queensland, 



XXIII (1911), 165. 



