GEOLOGICAL FEATURES. 261 



The ever-provident squirrel was observed arranging his nest 

 and storing his supplies in the cavities of the trees; more, how- 

 ever, against the long hot seasons than against the winter, as 

 with us. There were great numbers of silicified trees lying 

 about over the ground ; in one place there was discovered a 

 piece of palm transformed into oxide of iron, with the pores 

 filled with pure silica. These fossil trees lie upon soft gray 

 sandstone, containing banks of shingle, which forms the under- 

 lying rock of the country. The way led across the hills Vun- 

 gue or Mvungwe, which were found to be composed of various 

 eruptive rocks ; at one part we have breccia of altered marl or 

 slate in quartz, and various amygdaloids. The different forms 

 which silica was found to assume were truly remarkable. It 

 appeared in claystone porphyry here, in minute round globules, 

 no larger than turnip-seed, dotted thickly over the matrix ; or 

 crystallized round the walls of cavities, once filled with air or 

 other elastic fluid ; or it may appear in similar cavities as tufts 

 of yellow asbestos, or as red, yellow, or green crystals, or in 

 laminae so arranged as to appear like fossil wood. Vungue 

 forms the watershed between those sand rivulets which run to 

 the northeast, and others which flow southward, as the Kapopo, 

 Ue, and Due, which run into the Luia. 



The ground in the neighborhood of the Kapopo and the Ue 

 was covered with rounded shingle, which, being hidden by the 

 grass, greatly aggravated the miseries of the pedestrian march. 

 The difficulty was increased, too, by the network of vines which 

 hedged the paths on every side and spread almost impassable 

 snares across it. There were among these vines, however, great 

 numbers bearing wild grapes, some of which were so delicate 

 that they resembled greatly the cultivated varieties ; these are 

 eagerly appropriated by the natives, and the Portuguese have 

 found out the value of some of the varieties for making vinegar. 

 Indeed, the invitation seems to be extended quite encouragingly 

 to those interested in grape culture to think of Africa. Another 

 species of fruit which was found to be really "delicious" is 

 known as the mokoronga. Its abundance does not diminish its 

 popularity. The natives speak of it as " all fat," which they 

 mean shall convey the impression of excellence. Though these 

 plums are but little larger than a cherry they are greatly relished 



