TTIE FOOT PLATEAU .'^>01 



portion underlain by sliales; but, as there is a large scries of sedimen- 

 taries underlying the shales, there seems to be no reason for discrimina- 

 tion between the shales and the underlying elastics from a physiographic 

 standpoint. It seems best to consider all that portion of the plateau 

 covered by sedimentaries as one province, under the title of foot plateau. 



The sedimentary rocks of the coast, according to Muff, are as follows, 

 in the order of their occurrence : 



Raised coral reefs and Pleistocene sands (Kilindini sands). 



Unconformity 



Changamwe shales, limestone at the base. 



Mazeras sandstones, pLsolitic limestone near the top. 



Mariakani sandstone. 



Maji ya Chumvi beds. 



Taru grits. 



Unconformity 



Gneiss. 



The clastic rocks have been laid down conformably one upon the other, 

 and have been uplifted, tilted, beveled as one common unit. Their age 

 ranges from the Carboniferous (?) to the Jurassic. The shales, which 

 are the youngest of the series, it seems quite certain from fossil evidence, 

 are late Jurassic. The foot plateau has been canted over, depressed be- 

 neath the sea, and uplifted, and it is simply a raised coastal plain of 

 Mesozoic age. 



The plateau rises with some abruptness from the water level to a 

 height of 200 feet. This slope, as already indicated, is an old sea cliff; 

 at its base is a wave-eroded platform of varying width cut in the coral 

 rock. The shales wdiich lie exposed on this plateau front are soft and 

 easily weathered, thin bedded and thoroughly jointed, and are easily 

 acted upon by erosive agents. This portion of the area is, as a result, 

 maturely dissected and presents a series of round, knobby hills with steep 

 slopes, separated by numerous ravines. 



The work of erosion is performed quite largely by intermittent 

 streams, which have pushed their way headward into the interior from 

 the coast plain for a distance of 20 miles or more. The larger ravines 

 lie 100 feet below the inter-ravine spaces; numerous side ravines have 

 been developed, the whole forming a minute dendritic pattern. 



To the west of the shales are the older and coarser elastics ; these grits 

 and sandstones are harder and more compact than the shales and they 

 have a different topography. The transition from the shales to the sand- 

 stones is announced topographically by a relatively steep escarpment, 150 

 feet high on the average, known as the Xdunguni Hills. Differential 



