528 PEOCEEDINGS OF THE GrEOLOGICAL SOCIETY. [Feb. 2, 



nation. So, again, Dr. Junghuhn describes in Java numerous volcanic 

 mountains from 4000 to 12,000 feet high, from the highest summits 

 of which streams have flowed of trachytic or basaltic lava, and 

 hardened on their slopes. The volcano of the Isle of Bourbon has 

 emitted many very copious streams of glassy lava, which, in the 

 admirable engravings of Bory de St. Vincent's work, are seen to 

 encrust the sloping sides of the cone at an angle of at least 35°. 

 That great cone (fig. 11) is indeed formed almost wholly of such flows 

 of lava, gaseous eruptions being unfrequent, and its phenomena chiefly 

 confined to the welling-up of a very viscous and ropy lava, which in 

 some places has formed ''mamelons" or small cones 70 or 80 feet 

 high, and rising at angles of 60° and even 80° *, just in the manner 

 of the mud-cones of Macaluba, by the overlapping of one stream 

 upon another lazily flowing from the same central orifice : and pre- 

 cisely similar are the formations of Hawaii ; so also those of the Sand- 

 wich Isles, as described by Dana. In fact, there are, I believe, few, 

 if any, volcanic districts where examples of unquestionable lava- 

 streams consolidated at high angles are not to be found. 



Professor Dana, indeed, gives a sketch of an actual bottle- 

 shaped piUar of lava 40 feet high (see fig. 12), on the flank of 

 Mauna Loa, formed by the welling-up of a fountain-like flow of lava 

 in an upright column, composed of one exuding wave or jet of the 

 viscid matter congealing over another, until the excrescence reached 

 that height, thus showing that, under certain conditions of viscosity, 

 lava will congeal positively in an upright position, or at an angle of 

 90° t. He adds that there are many such on the s'ame mountain 

 (Mauna Loa), which is itself composed of repeated similar overflows 

 of very liquid but rapidly consolidating lava from the central vent. 

 Other lava-cones of great size in Tahiti are described by him as evi- 

 dently the product of the same kind of tranquil ebullition, — the erup- 

 tions of the Sandwich Isles being in general characterized by only 

 a small amount of explosive fragmentary ejections, but one overflow- 

 ing layer of lava covering another, and forming a cone composed 

 almost wholly of beds inclined at an outer slope of from 20° to 40°$. 



Support has been sought for the theory of upheaval in the circum- 

 stance that within the interior of some craters we find bulky bosses 

 or hummocks of trachytic rock, which are supposed to have been 

 elevated in a more or less solid state, and to have tilted up the over- 

 lying beds in an encircling annular range. Examples are oflered in 

 the craters of Astroni, the Camaldoli, Eocca Monfina, and Monta- 

 miata, in the district of Naples, in the Caldera of Palma, and that of 

 the Great Canary Isle, &c. There is, however, no good reason for 

 supposing the protrusion of such masses of trachyte to have elevated 

 the surrounding crater-walls. The felspathic lavas appear generally, 



* See fig. 14, p. 531. 



t In truth, the common fact of the congelation of even so perfect a Hquid as 

 water in a vertical position (as in icicles) ought to have suggested itself as a 

 warning to M. Elie de Beaumont of the weakness of his theoretical notion that lava 

 (a far less perfect fluid) could not congeal at a high angle of slope. 



I V. S. Expl. Exp. i. p. 356. 



