THE EAUDAL DE CARIBEN. 135 



the Middle Orinoco, By putting our ears close to their 

 surface we were able to detect low, musical tones, which 

 our guides observed were more audible in the early morn- 

 ing. The granite is split with deep crevices, that seem to 

 give emission to these mysterious sounds. Humboldt says 

 that he never himself heard these musical tones, but, re- 

 lying i;pon trustwoi'thy information as to the reality of 

 this phenomenon, gives the following explanation of the 

 cause : " It may easily be conceived that the difference of 

 temj^erature between the subterranean and external air 

 attains its maximum about sunrise, or at that moment 

 which is at the same time farthest from the period of the 

 maximum of the heat of the preceding day. May not 

 these organ-like sounds, which are heard when a person 

 lays his ear in contact with the stone, be the effect of a 

 current of air that issues out through the crevices? Does 

 not the impulse of the air, against the elastic spangles of 

 mica that intercept the crevices, contribute to modify the 

 sounds ? " 



By noon of the 18th we reached the liaiidal de Cariben, 

 where we encountered cataracts that could not be passed 

 Avith the paddle. The river was blocked with gi-eat masses 

 of granite, while huge bowlders strewed the shore, some 

 resting far back from the stream, and often nicely poised 

 one upon another. Traces of ancient water-levels high 

 up on the walls, which in places enclose the river, point 

 unmistakably to the time when the Orinoco was a mighty 

 stream, rolling its volume across the continent like an 

 ocean, but now reduced to the comparatively little rivulet 

 that courses through the bed of the former channel. In 

 those periods of greater floods these bowlder-like masses, 

 now at a distance from the river, were separated by de- 

 stroying forces from the rock upon which they rest, and 

 by the erosive agency of the waters were worn and left 

 in their present isolated and often strange positions. In 



