1883. | The Geology of Central Australia. 1131 
accordingly it is forced to the surface by hydrostatic pressure. 
Consequently there is a double line of springs following the 
outcrop of the schists (see figures ante). A great deal of 
the water flows on further south until it is obstructed by the 
Paleozoic rocks of the Flinders range, whereupon it comes to 
the surface, forming an east and west line of springs (see Fig. 4). 
The quantity of salts contained by the water varies a good deal, 
but is always considerable. The principal salts are the carbonates 
of lime and magnesia. The travertine deposits are immense, and 
in some places form hills 200 feet high. The general form of the 
hills is that of a truncated cone. On the summit is a clear basin 
of water fringed with rushes, and down one side a stream of 
bright clear water trickles, soon to be re-absorbed by the parched 
ground. Bubbles continually rise to the surface of the pool, and 
are generally caused by the liberation from the water of carbonic 
acid gas. In other cases it is marsh gas, derived by the de- 
composition of the vegetable matter in the pool. When the 
water issuing from a spring has built a mound up to a consider- 
able height, the pressure not being great enough to force it any 
higher, the travertine forms over the top, closing it completely, 
the spring then breaks out anew near its base. Mounds can be 
seen in every stage of evolution, from one the size of a bee-hive 
to one long deserted by water, standing alone like a huge melan- 
choly sentinel. In these mounds are found remains of Diproto- 
don, &c. The conclusion is plain that an abundance of water 
could be procured by artesian borings through the rocks occu- 
Pying the central desert, and possibly in this way the country 
May be developed in the future. 
The topography of the interior is dismal and monotonous to a 
degree. In every direction from Lake Eyre the land gradually 
rises. The sandhill country predominates around the lake, but 
occasionally there are patches of stony plains. Both the sand- 
hills and the intervening clay-pans are sparsely covered with low 
thickets or “ scrub” of Eucalyptus, Acacia, Melaleuca and Cryp- 
tandra. Along the watercourses a few stunted gum trees are 
found (Eucalyptus). The stony plains, though a little diversified 
by the table-topped hills, are even more desolate in appearance. 
rom north to east from the lake this is the character of the 
country for hundreds of miles. Ridge after ridge of sandhills 
Covered with Sparse vegetation, with here and there a dry aay- 
VOL. XVH,——NO. x1, r 
