1341.1 Capt. Huttons Geological Report. 2 1 1 



The upheaving lava current had therefore not only the weight of 

 the superimposed deposits, but the pressure likewise of an enormous 

 volume of water. It becomes more than probable, therefore, that this 

 aqueous pressure would effectually check the tendency to produce cinders 

 and ashes, and thus as the stream poured upwards through the deposits and 

 came in contact with the waters, the molten matter would extend itself 

 along the bottom of the lake, and thus overlie the secondary strata, 

 as in the present instance. 



For farther information on this subject, I would refer the reader to 

 De la Beche's Geological Manual, where will be found some very just 

 and apposite remarks on the point in question. 



" It being by no means probable," he says, "that the density of sea 

 water beneath any depth which we can reasonably assign to the ocean, 

 would be such as to render it of greater specific gravity than liquid 

 lava ejected from a volcanic rent, situated beneath the sea, it would 

 follow that so long as the lava continued in a state of fusion, it would 

 arrange itself horizontally beneath the fluid of inferior specific gravity." 

 The question then arises, how long a body of lava in fusion would 

 remain fluid beneath the waters of the sea? The particles of water 

 in contact with the incandescent lava would become greatly heated, 

 and consequently, from their decreased specific gravity, would immediately 

 rise : their places being supplied from above by particles of greater 

 density and less temperature. Thus a cooling process would be esta- 

 blished on the upper surface of the lava, rendering it solid. 



Now as the particles of fluid lava would be prevented from moving up- 

 wards by the solid matter above, pressed down by its own gravity and the 

 superincumbent water, they would escape laterally, where not only the 

 cooling process would be less rapid, from the well-known difficulty of heat- 

 ed water moving otherwise than perpendicularly upwards, but where also 

 the power of the fluid lava to escape resistance would be greatest. 

 ( See plate) — Fig. 4. Let a be a volcanic rent, through which liquid lava is 

 propelled upwards in the direction d f: the lava being of greater specific 

 gravity than the water b h e c it would tend to arrange itself horizontally in 

 the directions d b d c The surface b d c having become solid, the lava would 

 escape from the sides b and c, spreading in a sheet or tabular mass around ; 

 and this effect would continue so long as the propelling power at a was 

 sufficient to overcome the resistance opposed to the progress of the lava, 

 or until the termination of the eruption, if that should first happen."* 



This clearly stated theoretic problem may now be successfully reduced to 

 practice, and will correctly and exactly apply to the phenomenon under 



* De la Beche's Geological Manual, p. 125. 



