Of a Country on the Climate. 



213 



the grass withered, the quantity of water retained in the 

 gravel and sand is frequently considerable. This water un- 

 donbtedly flows very slowly and gradually to the rivers. 



With regard to the storm waters which fall on the plains, 

 it is necessary to mention, in the first instance, that the rain- 

 fall will be less, on the average, than that received on the 

 higher lands, even under the most favourable circumstances, 

 unless the plain be of very small area indeed. Notwith- 

 standing, a considerable quantity must fall during the year, 

 on plains south of the Dividing Range, and it is necessary to 

 inquire whether it reaches the river beds in the usual manner, 

 or is wholly evaporated, or is absorbed by the soil. 



Section No. 3, drawn across the Darebin Creek, represents 

 the edge of a plain of basalt, ending in a steep cliff. In the 

 rainy season the surface of this plain is very wet, and indeed 

 migiat be called a swamp. The soil is a loose black mould,with 

 a substratum of yellowish white clay; the depth of which varies, 

 being usually from one foot to ten feet. On examining one of 

 the quarries in that neighbourhood, I observed that the spaces 

 between the blocks of basalt were completely filled with this 

 clay, which in short, is due to the decomposition of the rock, 

 and is exactly what we might expect. Taking this circum- 

 stance into consideration, we may conclude that a very small 

 per centage of the rainfall will permeate such a stratum, and 

 that its loss may be accounted for by evaporation, and by de- 

 composition.* When we consider the character of the rock,, 

 its close compact structure, and the absence of large hollows^ 

 we perceive at once, that we must not look there for strong; 

 or permanent springs. It is true that feeble springs issue 

 from this rock, highly impregnated with iron, but they are 

 usually In situations where the basalt is decayed, or where 

 the shrinkage cracks are numerous and close together, f la 

 addition to this rock being unfavourable to absorption, it has the 



* A relatively small proportion of tlie rainfall is always decomposed^ and 

 the elements form plants — and, of conrse, that cannot again appear as water. 

 It would be curious to estimate the probable quantity thus lost, in the borders 

 of a reedy swamp, for instance, for comparison ; but in an inquiry of this kind 

 it is only necessary to consider what is lost by absorption, evaporation, &c. 



t This may seem at variance with the experience of many : — for instance, the 

 high ranges whence the Yarra River takes its rise, are composed of basaltic and 

 other igneous rocks ; and many small streams descend from these heights, which 

 are permanent, so far as they flow over impervious strata. This may be due to 

 the dense vegetation covering these hills, which, in a state of semi-decomposi- 

 tion, will retain moisture. I have had some conversations with Mr. Hodgkinson, 

 the District Surveyor, and with Mr. Daintree, the associate of Mr. Selwyn in 

 the geological survey, and the information which those gentlemen have so 

 generously afforded, has led me to take this view of the question. 



