60 HORN EXPEDITION — GENERAL GEOLOGY. 



Fossils were found in large numbers in this quartzite at and near the summit, 

 but they were all in the form of casts. The lowest point at which they were 

 obtained in situ was about twenty feet from the summit. Fragments, liowever, 

 were found luwer, but only in the talus. 



WinnaWs Ridge and the outcrops beltveen it and George Gill Range. — In the 

 journey from George Gill Range in a S.S.W. direction to Ayers Rock a number of 

 outlying portions of Ordovician strata were met with, surrounded on all sides by 

 red sand-iiills. About three-and-a-half miles from Reedy Hole, on the south side 

 of George Gill Range, the eastern extremity of a low sandstone outcrop was passed; 

 at eight miles from the same point a low sandstone ridge with an E. and W. strike 

 was crossed ; and at eleven miles our course led us past the eastern extremity of a 

 low sandstone range, striking in a W.N.W. and E.8.E. direction, the sandstone of 

 which had a dip of about 10° to the south. All these outcrops of Ordovician 

 strata are separated from one another, and from those about to be mentioned, by 

 red sand-hills, which entirely conceal from view the rocks which underlie them. 

 At twenty-four miles from Reedy Hole a low sandstone range, striking in a W. 

 35° N. direction was passed, ami at tliirty-one miles we journeyed within four 

 miles of an elevated, isolated hill lying W.N.W. of our track. 



The last and most important development of Ordovician rocks observed on 

 the trip to Ayers Rock was Winnall's Ridge, situated thirty-nine miles S.S.W. of 

 Reedy Hole, and nine miles north of Lake Amadeus at the point where we crossed 

 it, generally known as "Gosse's Crossing." This ridge rises to an elevation of 200 

 feet at the eastern end, where it was examined, and at the western end it appeared 

 to rise at least 100 feet higher. Its altitude above sea-level is probably from 1700 

 to 1800 feet. The strike of the ridge is W. 15° N., and its length about three 

 miles, its width at the base varing from 200 yards to a quarter of a mile. It is 

 composed of a dense grey quartzite, which on the northern face is observed to dip 

 southerly at about 25°, and on the south face to dip northerly at about the same 

 angle. The rock thus forms a synclinal trough, which fact is readily apparent 

 when the ridge is viewed in the direction of the strike. No fossils were found in 

 this quartzite. 



IV. — Post-Ordovician Conglomerate. 



The earliest reference to this formation is by Giles (iv., p. 17), and was 

 later traced by Chewings* west of Ellery's Creek to the head of Rudall's Creek. 



* The Sources of the Finke River, l)y Chas. Chewings, Adelaide, 188C, pp. 23 and 34. 



