286 EEACTION OF THE INTERIOR OF THE EARTH 



successively from 37 to 25 and 101. The ribs of the 

 volcano Gr. Tengger (8700 feet) are almost as regular ; 

 those of Gr. Ringgit have been in a great degree covered 

 over and destroyed by the devastating eruptions which 

 have taken place since 1586.( 418 ) The origin of these 

 very peculiar longitudinal ribs and of the intervening 

 clefts, of which drawings are given, are ascribed to 

 " erosion by torrents." 



The mean quantity of meteoric water in this tropical 

 region is indeed much greater than in the temperate 

 zone: the rain often falls in floods resembling water- 

 spouts; and although on the whole the quantity of 

 moisture diminishes in ascending higher in the atmo- 

 sphere, yet on the other hand great conical mountains 

 are powerful attracters of clouds, and, as I have shown 

 elsewhere, volcanic eruptions have a specific action in 

 exciting tempests. Phenomena in some degree analo- 

 gous are, indeed,presented by the clefts and valleys, called 

 barrancos, in the volcanoes of the Canaries and of the 

 Cordilleras of South America, described by Von Buch( 419 ) 

 and myself, which are important to the geological 

 traveller in giving him access to the interior of the 

 mountain, and sometimes even conducting him near to 

 the highest summit and to the escarpment surrounding 

 a crater of elevation; but although the barrancos at 

 times form channels through which the meteoric waters 

 are carried off, yet their first origin is not to be ascribed 

 to such waters. ( 42 ) It is probable that fissures result- 

 ing from the folding of the soft upheaved and only 

 later hardened trachytic masses preceded any effects 

 of erosion by the action of the water. But in the deep 

 barrancos on the declivities of domes or conical moun- 



