J. T. Jutson — Sheet-flows or Sheet-floods. 435 



Aet. XXIX. — Sheet-flows, or Sheet-floods, and their asso- 

 ciated phenomena in the Niagara District of sub-arid 

 south-central Western Australia; by J. T. Jutson. 



Introduction. 



Sheet-floods occur in arid and sub-arid countries, the 

 classical exposition from a physiographic standpoint be- 

 ing that by McGee 1 in regard to an area in North Amer- 

 ica. He attributes considerable erosive power to the 

 sheet-flood, but his conclusions have not been generally 

 accepted by American physiographers and geologists. 



Sheet-floods occur in the sub-arid portions of south- 

 central Western Australia, but so far as the writer is 

 aware, no detailed description of them has ever been 

 given, nor has their work in the role of erosion been dis- 

 cussed. The present paper is therefore a contribution to 

 the subject. 



It may at once be stated that the sheet-floods here dealt 

 with do not, in the writer's opinion, possess the erosive 

 activity attributed by McGee to the sheet-flood in the 

 area specially studied by him; but the writer does not 

 presume to question McGee 's conclusions for that area. 

 This paper is only concerned with the manifestation of 

 the sheet-flood in sub-arid south-central Western Aus- 

 tralia, as exemplified in the Niagara District. 2 The term 

 "sheet-floods," however, will not be used; "sheet-flows" 

 appear to be more suitable to describe the widespread 

 moving sheets of water as a whole, some of which are 

 quite gentle in their action, and could hardly be classed 

 as floods. 



Summary. 



Sheet-flows in sub-arid south-central Western Aus- 

 tralia are broad, shallow, but not necessarily continuous, 

 sheets of water, which traverse the gently-sloping sides 

 and the flat bottoms of wide, open, shallow valleys, and 

 the floors of plains. They are divided into three classes, 



1 McGee, W. J.: "Sheet-flood Erosion. " Bull. Geol. Soc. Am. vol. 8, 

 pp. 87-112, 1897. 



2 Niagara is a decayed mining township on the great sub-arid plateau 

 of Western Australia. It is 118 miles north of Kalgoorlie and is 1460 

 feet above sea-level. The average rainfall is slightly under 10 inches per 

 annum. 



Am. Jour. Sci. — Fourth Series, Vol. XL VIII, No. 238. — December, 1919. 

 30 



