Reviews— Geological Survey of 8. Australia. 279 



only place where the rocks are not highly altered is along the Tetti 

 Creek, where they consist of sandstones and slates. 



Pliocene Leads, Deep Leads, or made ground. — During the Tertiary 

 period, the main range was already elevated considerably and two 

 main streams flowed, one on each flank, into which small gullies pro- 

 bably ran. Both these creeks flowed north, as is proved by the level 

 of their old beds descending in that direction. The one on the east 

 side seems to have risen somewhere near Mount Gawler, thence flowing 

 in a northerly direction, its course being now traced by a few out-lying 

 patches of made ground, and by a general line of low country crossing 

 the present creeks. 



The other had its rise somewhere to the southward, and passed on 

 the west side of Mount Gawler, and flowed northward towards the 

 Humbug Scrub, where, at the head of Leg of Mutton Gully, it was 

 joined by the eastern stream. Thus increased in size, it flowed across 

 the present river to the Barossa goldfield, and so on in a north-westerly 

 direction to Gawler, where it discharged itself into the sea. This is 

 deduced from the position of outlying patches of Tertiary gravel, sand, 

 and clay (marked yellow on the map), which have escaped denudation. 



These deposits constitute the old gold drifts from which a consider- 

 able amount of gold has been obtained in Barossa, and a small amount 

 in Para Wirra. As the payable portion of these gold drifts can only 

 be ascertained by sinking shafts — often through hard conglomerate, 

 the gold occurring in gutters beneath — a considerable amount of labour 

 has to be performed before a run of gold is struck ; in consequence, 

 a large area consisting of patches of this Pliocene Tertiary has not yet 

 been prospected by the gold miner. Here and there a hole has been 

 put down, but only in a random manner ; and the ground still remains 

 unproved. 



The patches of old gold drift, which are known as "made hills," 

 are generally characterized by ferruginous sandstone and conglomerate 

 capping, called cement, which being very hard, has protected the 

 softer beds of sand, pipeclay, and gravel, from being washed away. 



In some cases the lower beds have been cemented, in which case 

 crushing mills had to be employed to obtain the gold. 



Para Wirra Gold Reefs. — General Notes. 



The Lady Alice reef has only been worked to a depth of about 

 160 ft., and is well worth being farther prospected below that level, 

 considering the richness of the stone already raised and the shallow 

 depth from which it was obtained. 



The various reefs and veins which are at the present time being 

 prospected on the Young Australian property show good prospects of 

 gold on and near the surface. They are worthy of a more systematic 

 and extensive examination by means of shafts. 



An examination of the map will show what a comparatively small area 

 of that occupied by Tertiary deposits of older gold-drift has been 

 prospected for gold. Shafts have been sunk here and there. Some of 

 these have not been bottomed, i.e. have not reached the bed-rock ; 

 others have bottomed on high ground, and the run of gold has not 

 been immediately struck, consequently operations have been suspended 



