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those, where travellers on the Oroonoko have 

 heard from time to time, toward sunrise, sub- 

 terraneous sounds, resembling those of the 

 organ. The missionaries call these stones laxas 

 de musica. " It is witchcraft (cosa de bruxas)" 

 said our young Indian pilot, who could speak 

 Spanish. We never ourselves heard these mys- 

 terious sounds, either at Carichana vieja, or in 

 the Upper Oroonoko; but from information 

 given us by witnesses worthy of belief, the exist- 

 ence of a phenomenon, that seems to depend on 

 a certain state of the atmosphere, cannot be 

 denied. The shelves of rock are full of very 

 narrow and deep crevices. They are heated 

 during the day to 48° or 50°. I often found 

 their temperature at the surface, during the 

 night, at 39°, the circumambient atmosphere 

 being at 28°. It may easily be conceived, that 

 the difference of temperature between the sub- 

 terraneous and the external air attains it's max- 

 imum 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 sounds of an organ then, which 

 are heard when a person sleeps upon the rock, 

 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 ? May 



