TERTIARY AND RECENT DEPOSITS 413 



Pan in the same district is about nine miles long and 

 five wide, while the Government's Pan between Stryden- 

 burg and Paauwpan Station is sixteen miles in length 

 and about two miles across. Pans from one to four 

 miles wide are very numerous. 



The material forming the pan floor varies consider- 

 ably in character. Sometimes it is a hard red clay a 

 few inches in thickness ; below this there is usually 

 shale. More commonly the soil is drab in colour and 

 somewhat porous ; in some of the salt-pans it is so soft 

 and powdery that one walks with difficulty over the 

 surface ; this character may be due to the effect of 

 capillarity when the last traces of saline water are being 

 evaporated by the solar heat. In some pans, especially 

 in those situated upon the Pniel diabase, there is a 

 powdery black soil, while if the underlying formation 

 is limestone there may be a good deal of porous tufaceous 

 limestone in and around the pan. 



There seems to be very little reason to doubt that the 

 majority of the pans have been excavated principally 

 through the agency of the prevailing northerly or north- 

 westerly winds. The bare soil in the pan becomes 

 finely comminuted, and frequently quite a gentle breeze 

 raises clouds of dust, while outside the pan the vegeta- 

 tion protects the ground to some extent and the sand is 

 not blown back in considerable quantities because there 

 are no suitable winds. 



It thus happens that the southern and south-eastern 

 edge of the pan is bounded by an area of fine light- 

 coloured sand sometimes forming dunes. Nowhere can 

 this be better seen than at the salt-pan between Douglas 



