! IlUKX EXPEDITION PHYSICAL GEOGUAPIIY. 3 



Thus (1) the McDoimell Ixan^es proper, as well as tlie Hart Range, are 

 situated wlioUy, or nearly su, within the area occupied by inetamorphic rocks of 

 presunialjly Pre-Cauibrian age ; wliile (2), the James, Waterhouse, George CJill, 

 and Levi Ranges are wholly contained within the country occupied by Ordovician 

 strata ; and lastly (3), tlie \o\v table-topped hills and groups of them, which one feels 

 disinclined to dignify with the name of mountains and mountain ranges, are entirely 

 formed of Ci'etaceous strata. Now, as each of these geological systems are repre- 

 sented l)y rocks ditleiing in lithological character and structure, while they have 

 suflcred diHeiently from tlie dynamic forces of nature, tlu^ physical features of the 

 ranges occupied by strata of these different geological systems differ widely, a,nd 

 will therefoi'e Ije described separately. 



(1) The McDonnell Ranges. 



Dealing with the features of the most important first, we find tliat the 

 McDonnell Ranges trend in a neai'ly east and west direction for a distances of 

 about 400 nules, and have a width varying from twenty to fifty miles, thus 

 covering an area of more than 10,000 square miles. 



In the meridan of Alice Springs Telegraph Station, which is situated from 

 three to four miles north of Heavitree Gap, where the River Todd breaks through 

 the southern ))oundary (jf the ranges under consideration, they have a width of 

 about twenty miles. 



Westerly fi-om this point they extend as a rugged main ridge, containing the 

 most ele\atrd peaks, often capped by Ordovician quartzite, with a band of varying 

 width of " jumbly " hills flanking this main ridge on each side. About the longi- 

 tude of Mounts Liebig and Palmer (i.e., about 131' IT)') the range becomes much 

 broken up. 



Easterly from Alici; S[)rings the range extends t(j about 136° east longitude; 

 at 131" 10' it Ix'comes confluent with the south-east extension of Strangways 

 Range, with wdncli it may be further eonsidcu-ed to be linked by the (ieorgina 

 Range, aliout 131° 20'; while further east (about 135") it is joined by Hart Range. 

 It may be said to extend approximately from tlx^ ]30tli to the 13(Uli meridian 

 of east longitude, a distance of nearly 400 miles, and to lii^ between 23° 7' and 23° 

 35' south latitude, with an average width of lietween twenty to thirty miles. 



These ranges have a very irregular outline, and have no parallel hmgitudinal 



valleys; in fact, they pi'esent in no degree that uniformity of physical features 



produced by earth movements and meteoi'ic agencies, so familiar in the case of tin; 



Ordovician ranges. 



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