1862.] THOENTON ZANZIBAE. 449 



Ugono this plain is narrowed to a neck ; but it again spreads out to 

 the west as the Great Plain of the Massai. 



Commencing at the coast, we have first a band, from 3 to 5 miles 

 wide, of coral-limestones and sandstone, &c., which is, I think, 

 of an early tertiary age. This formation is, in common with the 

 greater part of the country through which we passed, covered with 

 red earth, in which I have not seen any fossils. Then comes rather 

 higher ground, composed chiefly of yellow clay-shale; then the 

 coast-range, which varies from 600 to 1300 feet high, consisting of 

 flagstones and sandstones. In the former are many traces of fossils, 

 and thin layers of carbonaceous matter ; in these at Eabbai 1 found 

 a few recognizable indications of a kind of Calamite (?), similar to 

 those found in the coal-formation of the Zambesi. (The salt-water 

 creeks of Mombas run with deep water at high tide into the foot 

 of this coast-range.) 



The general dip of this sandstone-formation is slightly seawards ; 

 but at Rabbai it is throvm by faults in various directions. The 

 Shimba is about the highest part of this range, and presents a fine 

 escarpment, about 800 feet high, towards the interior. On the face 

 of this escarpment I found many blocks of silicified wood ; but ap- 

 parently the wood had been much decayed before being silicified. 

 From hence, until halfway to the Kadiaro, we passed over low ridges 

 of flagstones and shales, perfectly similar to those of the Zambesi 

 coal-formation. The dip was to the east at about 5°. These end in 

 a low escarpment, about 200 feet high, at the foot of which the 

 great plain commences (but is not very level). As far as Kadiaro, 

 where rock is seen on the surface, it is generally white sandstone, fre- 

 quently containing deep circular cavities, in which we often found 

 water. Beyond Kadiaro, metamorphism commences, ending to the 

 south-west in many detached unichnal ranges and hills of the meta- 

 morphosed sandstone-formation, fronting and dipping from the north- 

 east ends of the Pare and Ugono ranges. 



The high ranges bounding this plain to the north and south all 

 appear to be uniclinal, dipping to the east. The Pare range is, I 

 think, of old crystalline metamorphic rock, dipping to the east at a 

 high angle. The Usambara range has, I think, a base of the same 

 rock, capped by thick beds of the metamorphosed sandstone, dipping 

 shghtly to the east ; and the Bura range, judging from its outline 

 as seen from a distance, may have a similar structure. The eastern 

 part of the Ugono range is of stratified rock ; but the western is, I 

 think, composed of syenite. The Anusha range appears to be of 

 stratified rock, dipping to the east at a high angle. The Kadiaro is 

 a high, narrow, precipitous mountain, composed of old crystalline 

 metamorphic rock, in thick beds, dipping to the east at about 5°. 



AVe have not reached the axis of structure of Eastern Africa ; but 

 very far to the south-west from Kilema are seen, on a clear day, 

 three very high rugged mountains (as high as the Meru Mountain) 

 with conical tops, which, if not volcanic (and I think their sides are 

 too steep, and shapes too irregular, for ordinary volcanos), may be 

 composed of the axial granite. 



