68 
land surrounding it towards the sea entrance, mark a stage of rest 
in the gradual retreat of the sea water, and are absolutely similar 
to like sand hills and breakaways on the margin of many of the 
inland lake basins. 
But why, it will be asked, should we appeal to marine plana- 
tion, when the jieneplain might possibly be explainable as due to 
ordinary fluviatile i)lanation. There are several considerable rivers 
traversing the plain, c.g., the Shaw, the Coongaii, the Dc Grey, the 
Turner, the Sherlock, and the Yule. These all flow down across 
the plain, and at times after heavy rains they carry large Hows of 
water, and become wide powerful rivers, of great erosive cai)acity. 
Such rivers arc well-known to be potent agents in reducing the 
lower parts of their valleys to wide flood-plains, through which 
they meander with fretpiently changing courses, here cutting down 
into the bedrock, and there levelling U]) hollows by tilling them with 
sediments. doubt there is a certain amount of this action in 
the case of the rivers referred to, but in going through the district 
it did not appear to the writer that there was much evidence of its 
having been either extensive or long continued, certainly not to 
the extent of being the main agency in reducing the country to its 
l)resent stale of even planation. On the contrary most of the 
rivers appeared to be cutting down their beds, having generally 
fairly straight courses without meanders, and high banks on each 
side of wide beds capable of carrying the floods without overflow- 
ing on to the plains. Where the Shaw River was crossed near the 
■’Gorge” there seemed some appearance that the bed of the river 
was excavated out of alluvial material altogether, giving some sup- 
])ort to the hood-plain theory, but this might be equally well 
explained on the marine planation theory by supposing that the 
Shaw River debouching out of the mountainous country on to the 
edge of the shallow sea would form a considerable ’’fan" or “delta” 
of gravel, through which it would cut its way downwards as eleva- 
tion of the land led later on to retirement of the coast-line. So 
far as the writer's o])Servation of these rivers has extended, it 
would a])pear to be an allowable generalisation to make that they 
are all. from Bilbara southwards to the Murchison, engaged in 
cutting their beds more deeply into the plains which they traverse, 
and not in l)uilding (kxal plains. Conlining the instances to such 
ws have been personally visited, this would apply to the rivers just 
now mentioned, and to the Jones River, the Harding River at 
Roebourne. the upiier feeders of the Ashburton and (jascoyne 
Rivers crossed o]\ the route from Beak Hill to Nullagine. the 
branch of the Gascoyne River seen between Beak Hill and i\!l. 
Ivgerton. and the upper feeders of the Murchison River, seen on the 
south side of the Robinson Range. I'urther south, in the gold- 
fields districts, the streams are not usually traceable for great dis- 
tance as recognisable watercourses, but at Boison Creek and Jones’s 
Creek on the Leonora to Lawlers road, there are other good ex- 
