52 HORN EXPEDITION^GENEHAL GEOLOGY. 



eight miles from that place, the ti'ack emerges from the Ordovician Ranges, 

 through which it had led for that distance, on to Pre-Cambrian gneiss. To the 

 north, from two to three miles distant, a somewhat elevated quartzite range is to 

 be seen forming, in all probability, an outlier of Ordovician strata. To the south 

 another (juartzite range was seen, which probably constituted the northern limit of 

 the main Ordovician area. Between these two ranges the Ordovician strata have 

 been entirely removed, exposing the Pre-Cambrian rocks at the surface, which 

 have been eroded into characteristic low, rounded, " jumbly " hills. Eastward 

 from this last point the Ordovician rocks lie wholly to the south, the northern 

 quartzite range dying out after a short easterly course. 



At Ai'ltunga (Paddy's Hole) the northern boundary lies a mile or two south 

 of the mining township, its further eastern course is not known. 



Westward of Alice Springs the quartzite ridge, which marks the northern 

 limit of the Ordovician strata, continues to Mount Gillen, where it sweeps S.S.W. 

 (about). In this face is an opening known as Temple Bar Gap. The range 

 continues a. short distance south of this opening, and then turns westward past 

 Burt's Bluff; still further west it continues to Mounts Bonder and Zeil, and Belt 

 Range. The western boundary of this area is not known ; but judging by the 

 observations of Mr. Tietkens, these rocks extend across the West Australian 

 border. 



{c) Stratigraphical Relations. 



The lowest stratum of the Ordovician System found directly overlying 

 the Pre-Cambrian gneiss a few miles to the south of Alice Springs is a dense 

 grey quartzite (^ide Fig. 2 /;). The junction-line between this quartzite and 

 the gneiss, where not concealed by a talus of quartzite, is seen to be uneven, 

 and more or less undulating ; a fact which, coupled with the great funda- 

 mental differences of a lithological and structural character, evidently points to the 

 presence of a strong unconformability, separating these members of the Ordovician 

 and Pre-Cambrian Systems. The same features are seen in Belt Range, as indi- 

 cated by Che wings (xi.) at Haast Bluff, but not Haast Bluff of Giles. Here 

 friable gritty sandstones and quartzite, aggregating 1500 feet in vertical thickness, 

 repose in an east and west direction on an undulating surface of schistose rocks, 

 and over which they transgress in a south and north direction (see Fig. 3 and 

 Section from Mereenie Bluff to Belt Range). Similar appearances are presented 

 in Mount Zeil, as seen from a distance of three-and-a-half miles ; here a crown 

 of quartzite transgresses over schistose rocks, which have; conspicuous planes of 

 foliation dipping north at a high angle. 



