70 
Easterly from Alice Springs the range extends to about 136° east longitude ; 
at 134° 10’ it becomes confluent with the south-east extension of Strangways 
Range, with which it may be further considered to be linked by the Georgina 
Range, about 134° 20’; while further east (about 135°) it is joined by Hart: 
Range. It may be said to extend approximately from the 13th to the 136th 
meridian of east longitude, a distance of nearly 400 miles, and to lie between 
23° 7 and 23° 36’ south latitude, with an average width of between twenty to 
thirty miles. 
These ranges have a very irregular outline and have no parallel longitudinal 
valleys; in fact they present in no degree that uniformity of physical features, 
produced by earth movements and meteoric agencies, so familiar in the case 
of the Ordovician ranges. 
The original stratification of the once sedimentary strata and the joints, that 
were perhaps present in the original granites, have played to all appearances 
no part in the moulding of the present physical features out of the metamor- 
phic rocks, the age of which is gonsidered to be Pre-Cambrian. Rising 
abruptly out of the elevated area of the Macdonnell Ranges, with no linear 
arrangement, but irregularly distributed, are a series ot eminences, whose 
summits are in some cases, as in that of Belt Range and Mount Sonder, 
capped by a northern extension of Ordovician quartzite. ‘lo the presence of 
this protective covering, which has effectually warded off the levelling forces of 
nature from the underlying less weather-resisting metamorphic rocks, is 
probably due the comparative elevation of these peaks. 
Ranged in order west to east the altitudes above sea level of the chief peaks 
are as follows:—Mount Edward in Belt Range, 4,649ft.; Mount Heughlin, 
4,756ft.; Mount Zeil, 4,040ft.; Mount Sonder, 4,496ft.; and Mount Giles, 
4,210ft. 
The average elevation of the surrounding country is over 2,000ft. above sea 
level, so that these mountains are not so prominent as one might be inclined to 
imagine judging alone from their altitude above sea level. They are nearly all 
accessible, as the slopes are not usually very precipitous, except, for example, 
the Belt Range (Fig. 3). 
The movements of the earth’s crust, to which these ranges bear witness, were 
to a great extent of Pre-Ordovician age, and were continued, though much 
diminished in intensity, down to Post-Cretaceous times. During the earlier 
part of the Ordovician period the Pre-Cambrian rocks probably underwent 
subsidence, so as to allow of the depositicn of Ordovician sediment that originally 
covered much at least of the area now occupied by Pre-Cambrian rocks. Later 
they partook of the Post-Ordovician upheaval, which converted much of the 
area occupied by Ordovician sea into dry land. Later again this area has 
probably participated in the gentle and gradual Post-Cretaceous upheaval, to 
which are attributable the very slight undulations in the Desert Sandstone. 
The extreme metamorphism of the Pre-Cambrian rocks is to a great degree 
Pre-Ordovician ; but, as indicated by the gneissic character of much of the 
intrusive granites, it was partly at least contemporaneous with that of the: 
Ordovician quartzites, &c. As should, perhaps, have been pointed out pre- 
viously, the elevated area occupied by the Macdonnell Ranges forms a great. 
part of the northern boundary of the Lake Eyre Basin. In travelling svuth-. 
wards from this elevated region towards the centre of the basin, we descend by 
