438 J. T. Jibtson — Sheet-flows or Sheet-floods. 



covers or partly covers, according to the volume of the 

 water, the soil-covered flats. Along the latter, floating 

 vegetation in the form of leaves, twigs and small 

 branches of trees and shrubs is carried by the water, and 

 becomes caught at the base of the growing vegetation, 

 remaining there for a time as evidence of the width of 

 the flow of the water. When the rain ceases, and the 

 channels become relieved, the water on the flats tends to 

 gradually drain to the channels, but much is left as pools 

 which gradually disappear by soakage and evaporation. 

 The main function of the water outside of the channels 

 appears to be neither to corrade nor to transport but to 

 deposit fine detritus ; and thus to widen, raise and smooth 

 the general valley floor. This is due to the loss of veloc- 

 ity by the spreading out of the water, aided by the ob- 

 structing vegetation. The general scarcity — so far as 

 the writer's observations go — of pebbles on these flats, 



Fig. 1. 



Fig. 1. Cross section illustrating smooth-bottomed valley type of sheet- 

 flow. 



Shows bedrock below with surface debris on slopes above; in center, fine 

 detritus with occasional pebbles. It is to be noted that some sandy slopes 

 are almost free from rock debris. 



and in natural or artificial cuts through them, also indi- 

 cates the low transporting power of the water. This 

 scarcity of pebbles is in places in marked contrast to the 

 gently sloping sides of the valley, which may have abun- 

 dant rock fragments up to three inches in length on their 

 surfaces. 



The above statement is generally true for the class of 

 country described, but of course modifications may 

 occur, such as the surface being somewhat furrowed 

 instead of smoothed ; and minute soil-terraces may occur 

 where any slope exists. 



3. Furrowed-floor type. — This type is particularly 

 characteristic of some wide, treeless, or almost treeless, 

 salt bush and samphire flats, which form such a promi- 

 nent feature in the landscape. These flats may be sev- 

 eral miles wide, and in places lie between ridges which 

 tend to rise sharply from the plain, thus forming a broad 



