692 



PRINCIPLES OF STRATIGRAPHY 



lively level plain, but where herds are absent, as in the regions be- 

 tween Karibib, the Otyipatura and the Erongo, infested by the Hot- 

 tentot robber hordes, the country is much dissected by rain-water 

 streams. 



Passarge thinks that it is not too much to attribute to the de- 

 structive force of the great herds of vertebrates in semiarid regions 

 the principal role in the lowering of great regions and the produc- 

 tion of gently inclined plains free from river furrows, with rem- 

 nants of higher monadnocks such as the Inselberge of the Kalahari 

 (Passarge-6 : /jo-/?/). 



What is true of the modern herds of vertebrates must have been 

 equally true of the great herds of mammals of Tertiary time, and 





Fig. 133. White ants' nests of earth in Matto Grosso, on the plains of the 

 upper Paraguay. (After Branner.) 



perhaps to an even greater extent of the gigantic saurians of the 

 Mesozoic. Certain it is that by their activities these creatures have 

 furnished an immense supply of material to the winds, which would 

 carry it to other regions and deposit it as new sediment. Burrow- 

 ing mammals such as the prairie dog, rabbit, mole, badger, wood- 

 chuck, gopher and ground squirrel are also very active in tunneling 

 the upper layers of the soil and in transferring material from below 

 to the surface. The beaver may also be mentioned in this connec- 

 tion as a destructive as well as a constructive agent. 



The manner in which fish, feeding on corals and nullipores, pro- 

 duce fine coral sand and mud has already been noted. In like 

 manner Crustacea are known to be active in breaking up the skele- 

 tons of echinoderms and other organisms, thus producing lime sand. 

 Sponges and alga riddle shells and even rocks, forming winding 

 passageways, which render these masses more liable to destruction 

 by waves and other agencies. Similarly certain mollusca, Pholas, 



