140. Failure of the Yan Yean Reservoir. 
account for their enormous watershed, is the same which has 
led all other scientific men to the very opposite conclusion. 
If, according to their view, cultivation of the soil diminishes 
the rivers, England of all other countries ought to have the 
fewest and the smallest in proportion to the rainfall, and the 
extent of surface, whereas, it is exactly the reverse, and, in 
these respects Australia is the very antithesis of England. 
A barren, uncultivated and impenetrable soil, absorbs no 
moisture from the atmosphere, and is very unfavourable for 
the deposition of dew. 
Luxuriant vegetation absorbs large quantities of moisture 
during the day, and is most favourable for the deposition of 
dew in the-night, and the surface, being protected from the 
direct rays of the sun, is always cool and moist, and the rain 
readily percolates through the soil to supply springs and rivers. 
Mere surface water adds little to rivers, except in floods: it 
is that which percolates through the soil, and traverses either 
the superficial, or deep strata, that forms the principal and 
permanent supply of rivers. 
A compact and impenetrable soil, such as the Committee 
believe to be most favourable for river supply, is in reality 
the worst adapted for that purpose, and it is only in the 
immediate vicinity of rivers that mere surface water can 
reach them. 
The capillary attraction of the soil is too great to allow the 
rain water to travel over any extent of surface. The varying 
inclination of the surface also, and numerous other obstacles, 
oppose its motion. 
Their illustration of the great watershed of the Dandenong 
ranges is worthy of notice. Because the surface soil is ankle 
deep with water in wet weather, they conclude that the 
watershed must be very abundant, whereas, the opposite 
conclusion is the more legitimate deduction. The rain, which 
is so firmly held in the surface soil as to convert it into 
swampy or boggy ground, cannot reach the rivers at all. It 
remains there only to be evaporated and lost. It is the geo- 
logical formation of the ranges, and the close structure of the 
graniterocks, which prevents therain from draining through the 
soil, and gives rise to swampy and marshy ground, even on the 
sides and summits of the mountain, and the same condition 
occurs in the slate formation, as for example in the swamps 
above Yan Yean, where the water cannot readily percolate 
through the fissures, or where there is a subsoil of heavy 
stiff clay. 
