xii THE LOVO VALLEY 



171 



found on the lower slopes of Mount Mbatini (see page 173) are, as 

 I should have also remarked in the case of the basaltic andesite 

 above mentioned, a little altered, as is indicated by the existence of 

 calcite and viridite in the groundmass. 1 



From this instructive ascent of the Lovo valley we may learn 

 that whilst the mountain mass is formed, to a considerable depth, 

 of agglomerates with underlying submarine tuffs, the deeper seated 

 rocks exposed in the river-beds are massive intrusive rocks. The 

 overlying agglomerates have preserved the submarine tuffs from 

 destruction, and there is no difficulty in assuming that they also- 

 were accumulated under the sea, but in shallow water, as evidenced 

 by the character of the tuffs. I found no signs of alteration in 

 these tuffs, and except in the case of the small dyke above noticed 

 there is no sign of the dykes penetrating the agglomerates. We 

 have here a section into the heart of the mountain-range ; and 

 assuming that the large intrusive masses of basic andesites had 

 penetrated these deposits, there would certainly have been some 

 evidence of this in the extensive exposures of agglomerates far up 

 the mountain-sides. As it is, however, we find such rocks only in 

 the deeply excavated river-bed. If we imagine a submarine 

 volcanic mountain, or one but slightly raised above the surface of 

 the sea, to be subjected during a long period of emergence to 

 marine erosion, the " basal wreck " of the mountain would ultimately 

 be covered over by submarine tuffs and agglomerates. This is the 

 condition that seems to be presented here. 



I did not make the ascent of Koro-tambu, the other principal 

 peak of the Koro-mbasanga Range. This round-topped mountain 

 is well seen from the summit of Mbatini from which it bears N. 30 

 W. by compass. It is probably the peak marked 2,753 f eet m tne 

 Admiralty chart, and is connected with Mbatini by a saddle not 

 under 1,500 feet in elevation. 



Some of the most important features in the above account of 

 this district may here be emphasised. We have seen that in the 

 peak of Koro-mbasanga and in the Lovo valley agglomerates and 

 agglomerate-tuffs, several hundred feet thick, overlie sedimen- 

 tary submarine tuffs. In the last-named locality the deeper 

 massive basic rocks are also exposed ; and we may infer in both 

 instances that the agglomerate-formation is a submarine deposit 



1 They are blackish and somewhat compact (sp. gr. 2*67271) and have 

 very small felspar-lathes less than 'I mm. long. They contain both rhombic 

 and monoclinic pyroxene, and are referred to genera i and 13 of the hypersthene- 

 augite-andesites. 



