24: 



Geological Notes on the Upper Finke 

 River Basin. 



By Ciias. Ciiewings, F.R.G.S. 



[Communicated by Prof. R. Tate.] 



[Read June 2iid, 1891.] 



Plate X^ 



During the first three months of the present year I travelled 

 in zig-zag fasliion through and about the watershed of the Finke 

 River, which takes its rise in the ranges near the centre of Aus- 

 tralia ; and such observations as I then made I now present to 

 the Society, and in doing so, no one is so conscious as myself how 

 incomplete and imperfect my efforts have been. 



Pre-Silurian Rocks. 



These are found freely distributed throughout the length and 

 breadth of the MacDonnell Ranges. They extend to near the 

 Western Australian boundary on the west, and to the Queens- 

 land boundary on the east. On the south the wall-like range, 

 called the MacDonnell Range South, afterwards to be noticed, 

 limits them in that direction ; while to tlie north their extent is 

 not yet known. Throughout they are highly crystalline in struc- 

 ture, distinctly stratified, with a dip in general to the north at a 

 steep angle. Hornblendic rocks give the north side of the ranges 

 and outlying hills a black appearance — -on closer observation they 

 weather into rounded masses, and crack in all directions, often 

 circular. Mounts Hay and Chappie Ranges are composed of 

 this rock. Feldspar (probably oligoclase) exists in the district, 

 and I found garnets as well. Impure garnets form a constituent 

 part of the hornblendic schist, which is closely compacted, 

 massive, and intensely hard. 



From the appearance of these rocks, the contour of the country, 

 and the remarks made by the late W. C. Gosse and Mr. Charles 

 Winnecke, F.R.G.S., on the Reynold's Range, situated some 90 

 miles to the north, and the late Colonel Warburton's remarks on 

 the country to the westward and north-west, I am assured that 

 the country now known as the Burt Plain, and from that to the 

 Reynold's Range, has been denuded, and is now many thousands 

 of feet lower than it originally was. It probably averages not 

 less than 2,000 feet above sea-level. This land, which is now a 



