524. A CORRELATION OF CONTOUR, CLIMATE AND COAL, 



regions) to the same geocol, is indicated on the western side of 

 the divide. 



This fact — the higher than normal temperature on the Cassilis 

 Geocol, tending to a lowering of the rainfall — is directly trace- 

 able to the erosion of the river basin. 



A brief description of an actual general rainfall, its distribution 

 and l'easons for the latter, will serve to introduce a discussion on 

 the annual rainfall distribution (as affected by contour) in New 

 South Wales. 



The general rains of October, 1905, show in a remarkable 

 way the correlation between the three massifs and the three 

 areas of maximum rainfall (see Plate xlvi.). The hot moist 

 air from the north was raised by the more elevated portions of 

 the divide into cooler regions than at intermediate positions, 

 the result being indicated in the figure. 



However, it is with the local rainfall of the Hunter Valley 

 that we are more particularly concerned. 



The rainfall data for two type-years, 1900 and 1902, were 

 taken from the official publications, and isohyetals (lines of equal 

 rainfall) plotted on the stereogram. The annual rainfall for this 

 State lies near 24| inches. In 1902 the average was only 14 

 inches — this being a drought year. Tn 1900 the average was 

 27 inches, being considerably over the average. 



In Plates xlvii. and xlviii.for 1900-2 we see, as is natural, that the 

 isohyetal lines lie roughly parallel to the coast. The greatest 

 rainfall is experienced in the extreme North-East and in the 

 Kiandra districts. The former maximum is owing to the eleva- 

 tion of moist warm air (flowing south from the tropical seas) by 

 the Macpherson Range and adjacent portions of the New Eng- 

 land massif. The precipitation being the greater perhaps 

 since the air has not yet become still further heated by its contact 

 with land-masses at somewhat greater temperature than the 

 ocean it has left behind. The Kiandra maximum is largely due 

 to the high level of the Kosciusko area, which reaches cold portions 

 of the atmosphere where somewhat different conditions obtain. 



