816 J. T. Jutson: 



as a whole, the records, as noticed above, are scanty. Under 

 these circumstances, some details, which were noted by the writer 

 whilst engaged in geological work in the Niagara-Kookynie dis- 

 ti-iict, ,and, later, in thie. IGomeit Valie-Gk)ongarrie districtst^ may 

 be worthy of record. Tlie following notes are, therefore, based 

 on such observations, and relate only to the districts mentioned : 



General Description. 



In the districts just mentioned, the climate is sub-arid, and 

 the average rainfall is abouth 10 inches, or slightly less, per an- 

 num. Except on the surfaces of the " dry " lakes, there is gen- 

 erally some vegetation, but there is much bare ground between the- 

 individual plants. 



The dust whirls; vary much in height, and perhaps in diametej*. 

 Many are but a few feet in height and in diameter, whilst others 

 are hundreds, and probably thousands, of feet high, and per- 

 haps of considerable diameter. The writer, however, has no 

 criteria as to the diameter of the high whirls, but in all in- 

 stances, the diameter is small compared with the height. The 

 dust whirls are essentially moving columns or pillars.. The whirls 

 (as the table below shows) rotate clockwise (that is, in the direction 

 north, thence east, thence south, and thence west), and anti- or 

 counter -clockwise. The anti-clockwise direction predominates on 

 the records obtained. A change from one mode of rotation to the 

 other in the same, dust whirl has been noticed, and such change 

 has taken place more than once in the same whirl. 



High dust whirls may be practically vertical, or curved, or bent 

 at a high angle to the ground. The curving, or lending, doubt- 

 less indicates varying wind velocity at different altitudes. 



The dust whirls travel in different linear directions across the 

 country. This linear movement is usually rapid in whirls that 

 are close to the observer. It is difficult to form an opinion about 

 the velocity of distant whirls, and no estimate has been made by 

 the writer as to the actual velocity of near-by whirls. A low 

 whirl, as a rule, dies out within a minute or two,' but a high 

 whirl may be visible many minutes, or possibly some hours. 



A dust whirl, even a very small one, is quite violent in its 

 action. Dust, sand, grit, and old tins and other rubbish are lifted' 

 from, or driven along the ground with great force. When taken 



14. The Niagara-Kookynie area is about 115 miles, and the Comet Vale- 

 Goongarrie area about 60 miles north of Kalgoorlie. 



