CHAP. II. BLACK GLAZE ON ROCKS. 39 



that only a sorely cowed trader could bear it. They often 

 refuse to touch what is offered — throw it down and leave 

 it — sneer at the trader's slaves, and refuse a passage until 

 the tribute is raised to the utmost extent of his means. 



Leaving the steamer next morning, we proceeded on 

 foot, accompanied by a native Portuguese and his men and 

 a dozen Makololo, who carried our baggage. The morning 

 was pleasant, the hills on our right furnished for a time a 

 delightful shade ; but before long the path grew fright- 

 fully rough, and the hills no longer shielded us from the 

 blazing sun. Scarcely a vestige of a track was now 

 visible ; and, indeed, had not our guide assured us to the 

 contrary, we should have been innocent of even the 

 suspicion of a way along the patches of soft yielding 

 sand, and on the great rocks over which we so painfully 

 clambered. These rocks have a singular appearance, from 

 being dislocated and twisted in every direction, and 

 covered with a thin black glaze, as if highly polished and 

 coated with lamp-black varnish. This seems to have been 

 deposited while the river was in flood, for it covers only 

 those rocks which lie between the highest water-mark and 

 a line about four feet above the lowest. Travellers who 

 have visited the rapids of the Orinoco and the Congo say 

 that the rocks there have a similar appearance, and it is 

 attributed to some deposit from the water, formed only 

 when the current is strong. This may account for it in 

 part here, as it prevails only where the narrow river is 

 confined between masses of rock, backed by high hills, and 

 where the current in floods is known to be the strongest ; 

 and it does not exist where the rocks are only on one side, 

 with a sandy beach opposite, and a broad expanse of river 

 between. The hot rocks burnt the thick soles of our men's 

 feet, and sorely fatigued ourselves. Our first day's march 

 did not exceed four miles in a straight line, and that we 

 found more than enough to be pleasant. 



