494 GREAT SERPENTINE BELT OF NEW SOUTH WALES, 1., 



inclined, be horizontal, or dip more or less steeply to the west. East 

 of the serpentine, the strata are all greatly altered by pressure 

 They consist of slaty siliceous rocks, reddish banded cherts, and 

 red jaspers in which the traces of radiolaria can be faintly dis- 

 cerned, highly cleaved and altered spilite, sheared tuffs or tuff a - 

 ceous breccia, and rarely schistose conglomerate. Here and there, 

 lenses of very crystalline limestone are present. The radiolarian 

 jaspers are the main features, and form very prominent and con- 

 tinuous bands adjacent and parallel to the serpentine-line. The 

 whole is riddled with quartz-veins, which are very poorly developed 

 in the western portion. 



The term "serpentine-line" has been employed for the marked 

 line of fault separating these two portions, for though the serpen- 

 tine rock does not form a continuous band, it is developed chiefly 

 in this particular line, forming a row of intrusions, which may 

 vary in length from 100 yards to 30 miles, and in width, from a 

 few inches to nearly two miles. And wherever serpentine occurs 

 not on this line, it lies in the more disturbed rocks to the east, 

 forming sill-like masses there also. In only two or three minor 

 and exceptional instances has serpentine been found lying to the 

 west of this line, and, as will be explained, these occurrences are 

 not anomalous. 



In spite of this apparently sharp definition, the eastern and 

 western series are not entirely distinct. Among the rocks of the 

 eastern series, the metamorphosed equivalents of some western 

 rocks can be clearly seen, and, moreover, we may trace one horizon 

 which passes across the line from the unaltered west into the 

 altered east. The facts clearly show that, at the close of a long 

 period of sedimentation, heavy orogenetic pressure came from the 

 east, folding and metamorphosing the eastern series, but becoming 

 less and less effective towards the west. This pressure culminated 

 in the formation of a great plane of overthrust faulting (which is 

 unusually steep). This relieved the western side from this pres- 

 sure it was suffering, before the series had suffered any notable 

 dynamic metamorphism. The great fault-plane was the main 

 channel of ascent of the ultrabasic magma. The many intrusions 



