208 



time of the year/ 1 ) cause this highly siliceous rock to split 

 under the stress of rapid contraction. This effect is strongly 

 marked along the exposed edges of the table-topped hills, 

 developing a vertical face of fractured rock at the top of the 

 cliff, which may be from 6 ft. to 12 ft. in thickness. The 

 fragments split off from the parent rock, in this way, follow 

 the gravitational slope and slowly make their way to the 

 bottom of the scarp. The distance separating these residual 

 portions of the tableland may amount to a mile, or many 

 miles, but the broken fragments of the hard capping, that 

 once overspread the country, are left behind in the intervening 

 spaces. This is one of the most characteristic features of 

 Central Australia, The hard vertical faces of the escarpments 

 have received the name of the Desert Sandstone, and the 

 scattered stones derived from its waste, and which cover 

 thousands of square miles of territory, are the so-called 

 "gibbers." 



It is seldom that such large stones, possessing a fairly 

 good conchoidal fracture, are available for making stone 

 implements as is the case in the Desert Sandstone country. 

 Not only is the sandstone chaleedonized but the argillaceous 

 beds have, in some cases, been changed to a porcellanite, 

 which has been much used by the natives in making the 

 cutting-stone which is invariably attached to their womerah. 

 Implements made from this class of stone are always of small 

 size, while the chaleedonized sandstone lends itself to the 

 manufacture of larger implements. 



II. Authenticity of the Stone Implements. 

 The question may be raised as to whether the chipping, 

 in the case of the implements now under description, has been 

 caused by natural processes rather than by human workman- 

 ship. There are no circumstances in the case that would 

 suggest a natural origin. None, for example, such as might 

 have been derived from subsoil pressure and differential move- 

 ments or creep, as observed by Mr. S. H. Warren, in a section 

 of the Bullhead flint-bed [xxvin./ 2 ) p. 238]. In the tableland 

 country there has been, practically, neither local strain or 

 transport. The Desert Sandstone capping is generally under- 

 lain by a soft argillaceous bed that easily yields to the weather. 



(i) During a recent expedition into Central Australia under- 

 taken by Professor Sir Edgeworth David and myself, the diurnal 

 temperature, in July, on one occasion had an extreme range of 

 50° F. in the course of twenty-four hours ; the day temperature, 

 in the shade, reached 86° F., and the minimum, at night, 5 ft. 

 from the ground, was 36° F. 



(2) Numerals in small caps, refer to the Bibliographical Refer- 

 ences at the end of the paper. 



