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XY. On the Conversion of the Geyser-throats in Iceland 

 into Volcanic Vents. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN the ' American Journal of Science ' for July of the pre- 

 sent year, vol, xii. p. 25, in an interesting paper by Prof. 

 C. G. Rockum, entitled " Notices of recent American Earth- 

 quakes," the following passage, referring to the eruption of 

 Trolladyngja, in Iceland, which took place in January 1875, 

 occurs : — 



" Earthquakes preceded and accompanied an eruption of 

 the volcano Trolladyngja, in the central part of Iceland. 



" The volcanic disturbance appears to have begun by sub- 

 terranean thunders during December 1874, extending through 

 nearly two thirds of the island. Early in January 1875 earth- 

 quakes occurred in all directions ; and then an old extinct 

 volcano near Yatrayskud opened, and for four weeks continued 

 to emit ashes, lava, &c. When this eruption ceased, another 

 extinct volcano near Myvatu, 100 miles further north, opened 

 and continued in action for several weeks. Both of these 

 eruptions occasioned great destruction of life and property. 

 Early in March there seemed to be a general upheaval of the 

 earth in the whole central portion of the island. The ashes 

 from these and still later eruptions fell to the depth of several 

 inches on the coast of Norway in the latter part of April. 

 It is stated that ' the geysers have dried up since the eruption 

 began, and, instead of water, emitted quantities of hot smoke 

 and ashes.' " 



If the latter part of this account be correct, it appears to 

 me to lend support by actual fact to the views enunciated by 

 me as to the " mechanism of Stromboli," read to the Royal 

 Society in June 1874, and published in its ' Proceedings ' for 

 that year, to which I refer your readers, as I must not occupy 

 your space further than by stating here that I there attribute 

 the rhythmical action of Stromboli to the concurrence in the 

 same vent of a measured supply of heated water, or geyser, 

 with the ejecta of a volcano of small energy. My views were 

 objected to, with much vehemence of assertion, by the late Mr. 

 Scrope, unaccompanied, however, so far as I can judge, by a 

 single satisfactory argument. 



Rightly considered, the fact of the sudden conversion of the 

 geyser-throats in Iceland into volcanic vents seems to me to 

 afford support to the probability that the mechanism assigned 

 by me to Stromboli may truly represent the phenomena as 



