284 SOUTH AFRICAN LAKES. 



north of the Orange or Gariep River, is composed of hori- 

 'zontal limestone without petrifactions, clay-slate, sandstone 

 or quartz rock, granite, greenstone, serpentine, and pot- 

 Btone. The most remarkable geological feature of the 

 country is the horizontality of the strata, — thus intimating 

 their undisturbed state. 



Geological Survey of the Karroo Ground recommended.--' 

 To geological travellers we recommend a particular exa- 

 mination of the compact clay-ground called Karroo, which, 

 if a deposite from ancient lakes, may prove to be a tertiary 

 formation. The surface only of the Karroo ground has 

 been described ; for, as far as our information goes, no ac- 

 counts have been published of its internal structure and 

 arrangement. It is by the study of the structure and 

 arrangement of its layers, and the careful examination of 

 the minerals, rocks, organic remains (if any) it contains, 

 and its chemical composition, that we can acquire a dis- 

 tinct conception of its true nature. 



RIVERS. 



The rivers of Africa, as far as connected with those re- 

 gions of this continent described in the present volume, 

 have been already particularly considered. As much, how- 

 ever, still remains to be known in regard to them, we may 

 add, that the attention of travellers, in investigating their 

 natural history, should, besides their geographical distri- 

 bution, be directed towards the various circumstances 

 connected with their fall, velocity, quantity of water they 

 contain, their eddies, freshes, and bore, if any such occur ; 

 also, the nature of their beds, inundations, occultations, 

 temperature at the surface, or at different depths ; their 

 cascades and rapids ; their water, as to colour, trans- 

 parency, and chemical composition ; and they should not 

 omit descriptions of the river scenery considered by itself, 

 and also in reference to the surrounding country ; and, lastly, 

 the climate, and effects of the climate, and of the scenery 

 of the rivers, on man, ought also to form objects of inquiry. 



SOUTH AFRICAN LAKES. 



In Southern Africa, lakes are but seldom met with, and 

 among these, some few are salt. The most considerable 

 •alt lake hitherto met with by travellers, is that near to 



