IIOUN KXI'ICDITION SUMMARY. IG") 



inolialily an iiilicr of I'rC'Ca.iiibi iaii locks. To tlic soutli oi this valley lisc twd 

 j)aiall(l lid^L'S of (|iiail;«tc, enclosing between them tiie Horn Valley, along vvliicli 

 outciu|is a, Ijand of limestone the existence of which has pioljahly determined the 

 line of (lemidation which has given rise to the va,lley. Forniing the northern 

 lioundary of the Ijroad Missionary Plain and resting uncunforniahly ujx^n the 

 (|iia-rtzite of the .southern of tJie two ridges Just mentioned lies a Ijed of Post- 

 ( Jidovician conglomerate. 



The ()rdo\'ician sti'ata, ha,ve been thrown into a scries of f(jKls, tho.se of the 

 northern ])art having lieen subjected to greater disturbance tliaii those of tiie 

 .south. 



Thus the L(!vi Range consists of sandstones dipping at low angles — about 8" 

 or l(J — to the south on the north sidt; and at about the same angle to the north 

 on the south side, the i-ange Ixnng thus formed out of a gentle synclinal trough. 

 In the north, in tlie James Ivange and at Mount Bonder for example, the strata, 

 have sulle.i-ed much greatei' disturliance, the (juartzites dipping at very high angles. 



The folding has been produced along lines running in a general east and west 

 direction and " the chief factors in aildition to the position of the longitudinal 

 valleys occupying the oi'iginal troughs of the folds, that have intluenced the 

 direction of the lines of denudation are (1) the lines of weakness on the crowns of 

 the anticlinal arches and (2) the position of the bands of limestone. An example 

 of the inlluence of (1) is furnished by the valley of the Peterniann Creek, which 

 has been eroded out of an anticlinal aicli, while the rocks of the corresponding 

 synclinal trough now form the (ieorge Gill and Levi Ranges. The inlluence of (2) 

 as might have been expected is to be observed throughout this region, the greater 

 nvurdjer of the \alleys within these ranges having been, to a great extent, eroded 

 out of the limestone beds."* 



The gorges and gaps through which the main stream flows across the successive 

 ridges, with rocks of (|ua.rtzite and sandstone rising almost vertically to In^ghts 

 varying from 200 to (SOO feet above the valleys, owe their origin to the fact that 

 the (U'osion of the river beds in the position of the; present gaps kept pace with the 

 uphiMval and folding of the strata. ]jy a gradual lowering of their channels as 

 the rocks ro.sc the streams have been able to maintain their original course, so that 

 the characteristic feature of the streams flowing over the Ordovician area is the 

 fact that I hey do n(jt follow the trend of the main valleys but run at right angles 

 to these. 



* Part III., Physical Ocogi-iipliy, p. C. 



