BY G. H. HALLIGAN. 631 



stirring up the sand and leaving it more fit for transportation by 

 the littoral currents. Currents of considerable velocity may 

 flow over sands without disturbing them, but if these sands are 

 broken up or agitated they will be transported by a current of 

 less velocity.* 



It is thus evident that, on this coast, the alongshore wind 

 which happens to be blowing during flood tide — although the 

 flood tide has no current in itself — will have a greater effect in 

 the movement of sand and shingle than a very much stronger 

 wind blowing during ebb tide. 



It must also be apparent that, as the S.S.E. littoral current on 

 this coast, though a slow one, is accelerated by northerly 

 winds and retarded by southerly winds, and as the winds 

 from the north-east quadrant are the prevailing winds on this 

 coast, the littoral current will be accelerated more often than 

 it will be retarded or reversed. The winds from the south, 

 although much stronger than those from the north, have to 

 expend so much of their energy in reversing the littoral current 

 that they cannot be termed the dominant wind, so far as the 

 movement of beach-material is concerned. In the matter of the 

 formation of sand dunes, the southerly winds undoubtedly 

 predominate, and there are many instances of this on almost any 

 sandy stretch on this coast. Perhaps the best and most access- 

 ible example is near the mouth of Tuggerah Lake. The so-called 

 Tuggerah Lake is really an estuary. The entrance is rarely 

 closed, and while it is open there is a small astronomical tide in 

 the lake. The same remarks apply in the case of Lake Illawarra, 

 Myall Lakes, and other similar formations on the coast. f 



The entrance in this case has been forced to the south by the 

 littoral drift, accelerated by the prevailing winds, until a rocky 



* Wheeler, W. H. , "The Sea Coast"; also Haupt, L. M., "Littoral 

 Movement on the New Jersey Coast," Trans. Amer. Soc. Civil Engineers, 

 Vol. xxiii., 1900. 



t Report by the author on " Tidal Investigation at Lakes Taggerah and 

 Illawarra," Public Works Department Records, January, 1906. 



