LATE PALAEOZOIC FOLDING IN THE HUNTUR RIVER DISTRICT. 135 



shell varying in thickness from 8 miles to 41 miles. This 

 deformation produced a crustal shortening of 7*46 miles in 

 a section 70'5 miles long. 



A comparison with the American areas is fitting here. 

 The comparison can be made along two lines chiefly, viz., 

 concerning the crustal shortening and the nature of the 

 folded shell. 



In the Appalachians the folding effected a shortening in 

 the earth's crust of 15 miles in 66 miles. The Rocky 

 Mountain folding in Colorado was such that, after thrust- 

 ing, the section which was originally 140*69 miles in length 

 became 132 miles long. The Hunter area, therefore, 

 displays diastrophism of intensity intermediate between 

 these two American areas, in that a strip 77*96 miles long 

 was reduced by 7'46 miles. Also in this connection it is to 

 be noticed that the folding in the Lower Hunter district 

 is of a fairly open type, there being no examples of true 

 overfolding. 



Regarding the comparison of the folded shells it is 

 interesting to notice certain general conclusions drawn by 

 Chamberlin concerning the relation between the intensity 

 of the folding and the nature of the disturbed zone. 



He found that mountain ranges, where the folding has 

 been intense and the crustal compression consequently of 

 a high magnitude, have been produced by the crumpling of 

 a relatively thin shell, and are characterised by the absence 

 of any great vulcanism which is resultant upon the dias- 

 trophism. Mountain tracts, on the other hand, which 

 display open folding, the absence of thrust faulting, and 

 the presence of strong resultant vulcanism represent the 

 product of the deformation of a very thick zone. With 

 regard to these generalisations it can be said of the Hunter 

 folding that a comparatively thin shell was involved, and 

 associated with this shallow zone is the evidence of fairly 



