116 



The author next adverted to the phenomena of earthquakes ; and 

 leferrinor to the Gi'eat Geyser, the eruptions of which, at the time 

 when he saw it, were preceded by sounds resembling the discharges 

 of artillery, and trembling of the ground, he inferred that the noises 

 and shaking of the ground during earthquakes, were caused in the 

 same manner in great cavities, such, most probably, as those which 

 contained the materials for trap or volcanic tuff. The cause of the 

 noises the author conceived tc be the occasional production of masses 

 of steam, reaching the upper and colder portions of the cavity, or 

 coming in contact with water and being suddenly condensed, so as to 

 produce a vacuum with extreme rapidity, the collapse, on its being in- 

 stantly filled up, causing sound and concussion. To explain this part 

 of the subject, he referred to a paper on sound, which he had read to 

 the Society some years before, and part of which will appear in the 

 number of Jameson's Journal for April 1847. 



The author next proceeded to extend the hypothesis of Mr Hop- 

 kins farther ; and endeavoured to shew, that the operations going on 

 within the cavities would necessarily go on extending their dimen- 

 sions, and weakening their roofs. This weakening would be greatly 

 increased by the eruption of the contained matter, and the enormous 

 masses of igneous rocks existing in volcanic districts and elsewhere, 

 proves that proportional spaces nmst have been left empty under- 

 neath. Vast tracts of land by being thus undermined may have sunk 

 and disappeared under the ocean. Several geologists have supposed 

 it probable, from various facts, that Europe and America were once 

 united, the Northern Atlantic having been occupied by land. This 

 being admitted, the author referred to the probability of the sinking 

 of the land having been caused (perhaps in large portions at different 

 periods) by the extension of such cavities as those which Mr Hop- 

 kins has supposed to exist, and to their roof giving way. The Britisli 

 Islands, the Faroe Island, and Iceland, may be regarded as remnants 

 of the lost continent ; and the latter island exhibits the strongest possi- 

 ble indications of preparation for the catastrophe of its disappearance. 

 The precipitous shores of these remnants prove that violent fracture 

 had taken place ; and that this island had been more elevated at a 

 former period, is rendered probable by the exceedingly shattered 

 condition of their rocks. Admitting this, and the extension of the 

 land over the Atlantic, the climate of Britain must formerly have 

 been severe enough to produce glaciers, which have left those marks 

 M'liich have been ascribed to them. 



