209 



As the latter wastes the harder stones on top are gradually- 

 let down to a lower level. Even in the case of the scarps, 

 flanking the "table-tops," the slope is gradual and could give 

 no gravitational impact that might cause a vibration equal to 

 a cause of fracture. Again, the Desert Sandstone is coarser 

 in the grain than the chalk-flints and does not so readily 

 fracture by compression. In a field of gibbers one stone does 

 not press against another, nor are they heaped together, but 

 evenly strewn over the surface where they were left by the 

 slow removal of the more friable bed on which, they rested. 



The shapes exhibited by these gibber stones have arisen 

 from various causes. The process of silicification has often 

 been partial in its operations, causing peculiarities of shape 

 and differential weathering. Sola.r influences and rapid 

 changes of temperature tend to the breaking up of the siliceous 

 rocks. This may occur under two forms. On a larger scale 

 the rocks are split, in situ, in a way that simulates jointing; 

 and, in a minor way, circular depressions sometimes occur on 

 a smooth faoe of rock, as though sun-flaked, and has probably 

 been so caused. In the case of the stone implements collected 

 from the gibber country, there are sufficient evidences of 

 design in their workmanship to prevent any mistake being 

 made between the sun-flaked and the man-flaked. In the 

 former case the features are those of circular or oval 

 depressions that occur on the face of the stone, either oddly 

 or without any definite order, while in the worked implements, 

 even where a naturally-shaped stone is used, there is evidence 

 of selection in the general shape of the stone and intention in. 

 the chipping. Except in the case of oval-shaped implements, 

 there is a thick edge, or butt, at one end, which is unchipped, 

 suiting the tool to the hand, while the lateral edges are 

 trimmed in such a way as never occurs with sun-flaking. This 

 is seen in the number of chippings (amounting to scores in 

 some examples) that have a uniform size and lineal direction, 

 along the edge, and, at times, are supplemented by a few 

 chippings on the under-side of the edge where it was needed 

 to secure a straight cutting edge. 



III. Description of the Tableland Implements. 



(a) GENERAL FEATURES. 



1. The implements that have been secured under the 

 circumstances already explained, can be separated into two> 

 divisions: — (1) Those that have been struck off as a fragment 

 from a larger mass, or core, and show conchoidal fracture with 

 a bulb of percussion. Examples belonging to this division are r 

 usually, smaller and better finished than those mentioned in 

 the following section. (2) Implements that have been 



