261 



the surface and finds its waj' b}?^ a rapid subterranean de- 

 scent through the thick alluvial that has choked the one-time 

 main waterway. These conditions are extremely favourable 

 for artesian water on the plains. The Orroroo bore proved 

 "that good water rose to the surface from a depth of 350 

 ft., and at the lower levels of 380 ft. and 502 ft. The most 

 abundant su.pplies would probably be tapped at the base of 

 ■the alluvial, resting on the bedrock. 



W. H. 

 Royal Society Meeting, 



October 5, 1909. 



EXPLANATION OF PLATES XVII. AND XVIII. 



Plate XVII. 



Fig. 1. — A view in Pekina Creek, nearly a mile above the 

 Irrigation Weir. The bed of the creek is encumbered by very 

 large blocks of Tapley Hill slates, which were laid there before 

 i;he lacustrine period. The lake-silt formei'ly covered these stones, 

 remains of which can be seen forming cliffs on the left bank, 

 the stream having washed out most of the lake deposits from its 

 immediate channel. 



Fig. 2. — A reproduction from a photograph taken about mid- 

 way between the Weir and the head of the Old Lake, shown in 

 •fig. 1. Standing back from the creek, on the right bank, is a 

 prominent ridge of lacustrine silt that has been weathered on all 

 ■sides. The beds show horizontal stratification and calcified reeds, 

 and Chara remains may occasionally be recognized amongst 

 its material. 



Plate XVIIT. 



A panoramic view of the alluvial terraces, about a mile below 

 the Weir, near the nlace where the waters of the creek disappear 

 from the surface. On exposed and sloping faces the alluvial ter- 

 races are quite bare, and the sides are cut by numberless water- 

 channels. On the extreme left side of the picture is the terrace 

 which is capped by a Chora limestone, described in the Postscript 

 ♦of the paper. 



