Physiography of Werribee Area. 189" 



of moisture; this sudden change in level takes place along an almost 

 north-south line, referred to in this paper as the Rowsley or 

 Bacchus Marsh scarp. 



An interesting and independent corroboration of this point is 

 afforded by the observations of Mr. R. Dugdale, of Bacchus Marsh. 

 Mr. Dugdale has a very extensive knowledge of the whole of the 

 area, from the point of view of land values, and informs the writer 

 that local land buyers have long recognised a '' dry belt" passing- 

 from a little east of Anakie through Nerowie, Mt. Cotterill, and 

 Melton, almost parallel to the coast. This is a matter of economic 

 interest, and the explanation of this dry belt appears to be as stated' 

 above. 



(b) Evaporation. — Mr. H. C. Wilson, Manager of the Government 

 Research Farm, suppliesi the following records of evaporation from' 

 a free water surface, taken at that farm, near the town of Wer- 

 ribee : — 



Year Rainfall Evaporation 



1913 - 16.43 inches - 46.43 inches 



1914 - 13.24 „ - 50.54 



1915 - 15.55 „ - 51.75 



For the three summer months of the former two years, the average 

 monthly evaporation was as much as 7.11 inches, while for the 

 winter periods the average was 1.44 inches. During the same 

 period the average daily amount of '' bright sunlight " for the 

 year was 5.2 hours. For the three winter months the daily average 

 was 4.0 hours, and for the summer period 7.6 hours per day. 



It will thus be seen that evaporation is probably an unusually 

 predominant factor in the disposal of the rainfall in these wide vol- 

 canic plains of the lower Werribee. The soil is generally some- 

 what clayey, and except after a very dry period when the soil 

 cracks are widely opened, the percolation would be small, similarly 

 the drainage is poor, swamps are common, and the run-oflt would 

 be comparatively low. With the dry conditions, and the level 

 nature of these plains, irrigation is naturally suggested, and we- 

 find that two of the most important farms of the State (the Govern- 

 ment Research Farm and the Metropolitan Board Farm) are 

 situated here. Both these farms are on a large triangular patch of 

 river-built material, the soil of which is largely basaltic in origin,, 

 although much more sandy and porous than if wholly basaltic. 



