69 
of one of the highest folds into which the crust of the earth within this area 
has been thrown. In the crumpling of the earth’s crust the highest anticlines, 
being on the lines of maximum disturbance, usually have cores of plutonic 
rocks. This seems to have been the case with a great portion of the Macdonnell 
Ranges, subsequent movements having metamorphosed the originally plutonic 
rocks, thus causing doubt as to their eruptive origin. 
The mountain system of Central Australia does not consist alone of the Mac- 
donnell Ranges and those immediately associated with them to the north and 
north-east, as the Hart and Strangways Ranges, but includes also a number of 
parallel ranges lying to the south, such as the James, Waterhouse, George Gill, 
Levi, and Chandler Ranges, all representing the arches or troughs of the folds 
produced by earth movements in past geological time. Examples of ranges 
occupying the troughs of the earth-folds are to be found in the case of the 
George Gill and Levi Ranges. In each of these ranges, which really are 
portions of one and the same range (their continuity being broken merely by 
the transverse valley of Trickett Creek, a tributary of Petermann Creek, the 
latter a branch of the Palmer), the rocks occupy a perfect synclinal trough, in 
which the sandstone dips from the north and south towards the centre of the 
range at an angle of from 10° to 20°. 
The mountain system of Central Australia may be conveniently treated in 
three divisions, the mountain ranges in each division for the most part com- 
prising rocks of one and the same geological age, while they differ from those 
of the other divisions. 
Thus (1) the Macdonnell Ranges proper, as well as the Hart Range, are 
situated wholly, or nearly so, within the area occupied by metamorphic rocks 
of presumably Pre-Cambrian age; while (2) the James, Waterhouse, George 
Gill, and Levi Ranges are wholly contained within the country occupied by 
Ordovician strata; and lastly (3) the low 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 Cretaceous strata. Now, as each of 
these geological systems are represented by rocks differing in lithological 
character and structure, while they have suffered differently from the dynamic 
forces of nature, the physical features of the ranges occupied by strata of these 
different geological systems differ widely, and will therefore be described 
separately. 
(1) THe MacponnELL RancEs. 
Dealing with the features of the most important first, we find that the Mac- 
donnell Ranges trend in a nearly east and west direction for a distance of 
about 400 miles, and have a width varying from twenty to fifty miles, thus 
covering an area of more than 10,000 square miles. 
In the meridian 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 boundary of the ranges under consideration, they have a 
width of about twenty miles. 
Westerly from this point they extend as a rugged main ridge, containing the 
most elevated peaks, often capped by Ordovician quartzite, with a band of 
varying width of ‘‘jumbly’’ hills flanking this main 1idge on each side. 
About the longitude of Mounts Liebig and Palmer /i.¢., about 131° 15’) the 
range becomes much broken up. 
