526 A CORRELATION OF CONTOUR, CLIMATE AND COAL, 



These huge eddies of air, moving over Australia from Perth to 

 Sydney at a rate of some 400 miles per day, occasionally appear 

 to be arrested by the Blue Mountain massif, perhaps for a day 

 ■or so. As Professor David graphically puts it, when lecturing 

 on this subject, " the preceding anticyclone having marched on 

 ahead, a tension between the two areas of high pressure may be 

 pictured, resulting in a sort of snap in the isobars. This may 

 give rise to a ' Southerly Burster ' from the south towards the 

 abnormal low pressure thus produced," while the increasing 

 pressure on the western slope of the divide causes the detained 

 anticyclone to be deflected somewhat to the north; where it is 

 able to cross the relatively low levels of the Cassilis Geocol. 



We thus see that even the grand westerly drift of the anti- 

 cyclones may be vitally affected by the variations in land-surface 

 due to river-erosion. 



Before closing this contribution to the physiography of the 

 State, brief mention may be made of another interesting allied 

 question, although it does not fall under the head of a correlation 

 of contour, climate and coal. 



FerreVs Law and the Rivers of the Western Plains. — A highly 

 interesting feature indicated by the stereogram is the constant 

 tendency of the Murray tributaries to curve towards the left. This 

 was pointed out when the model was exhibited in November, 

 1905, and a possible explanation is as follows : — According to 

 Ferrel's law, all bodies (including water) moving in the southern 

 hemisphere have a tendency to curve to the left. Other writers 

 have brought forward examples of such river-curvature (cf. Obi 

 and Yenesei in the Siberian tundras), and it appears to me that 

 in the flat alluvial plains of the Murray-Darling system there 

 obtains an ideal state of affairs in this connection. The Macintyre, 

 Gwydir, Lower Castlereagh, Lachlan and Darling itself seem to 

 show that there has been a greater tendency to erode the left 

 bank than the right, giving rise to a gradual curving to the left. 

 The rivers are several hundred miles in length, and the water 

 necessarily passes across portions of the earth's surface which are 



