350 Analysis of Scientific Books and Memoirs. 



1720, and 1811 ; of Santorini, and the Isola Nuova in the Archipelago; 

 another off the coast of Iceland in 1782; and one amongst the Aleutian 

 islands in 1814. But, on reflection, we must conclude, that the weight 

 of the water above the vent, arid the refrigerating effect of its contact, 

 must, in all cases, condense the escaping volumes of steam, and prevent 

 their rising to the surface, and rendering the eruption visible there, except 

 when the orifice of the volcano has been raised by the accumulated pro- 

 ducts of repeated eruptions, to within a short distance of that level ; so 

 that numerous eruptions may be continually taking place within the depths 

 of the ocean, without our being aware of their occurrence in any way. 

 There is no reason for concluding such eruptions to proceed in any very 

 different manner from those which are subaerial. The expansive force 

 and temperature of the lava must be extreme, and proportioned to the great 

 excess of the repressive force occasioned by the pressure of the supported 

 column of water. The lavas, when emitted, will, therefore, from the in- 

 tensity of their temperature, and the resistance opposed by this dense me- 

 dium to the exudation of the confined vapour, retain their fluidity much 

 longer in the open air, and, consequently, spread laterally to a far greater 

 distance from the vent, with a similar inclination of surface. According 

 to this, lava-beds, produced at the bottom of the sea, ought to exhibit a 

 greater lateral extension, compared with their bulk, than those which 

 have flowed from subaerial volcanos ; and, in fact, the great horizontal 

 dimensions of the flcetz-trap formations of Ireland, Germany, Iceland, 

 Faroe, the Hebrides, &c. have long been a subject of remark. Again, 

 since little or no vapour can escape from the surface of the lava, such beds 

 should show very few scoria; or scoriform parts on their upper surface ; 

 and, on the contrary, vesicles, or air-cells, may be expected often to abound 

 through the interior of the rock, the extreme tension of the steam causing 

 its parcels to expand as the lava flows on, while the rapid consolidation of 

 the surface, and the weight of the sea above, must prevent their rising up- 

 wards. 



These characters also accord with the appearances of many of the flcetz- 

 trap rocks, amygdaloids, &c. which seem clearly to be the products of 

 submarine vents. Of the fragments thrown up by the explosions of sub- 

 marine eruptions, some will accumulate round the orifice in rude beds, 

 others be dispersed by currents, and mixed or interstratified with other 

 marine deposits. In the north of Italy and Sicily, are frequent examples 

 of ealcareo-basaltic conglomerates, (peperino) as well as of beds of basalt, 

 alternating repeatedly with compact limestone strata. The hills of the 

 Phlegraean fields near Naples, the author supposes to have been thrown 

 up by subaqueous eruptions from a very shallow shore, which has been 

 subsequently elevated above the sea-level, by subterranean expansion. 



When the summit of a submarine volcano is raised above the surface of 

 the sea, it conforms to all the laws, already investigated, which regulate 

 the conduct of a subaerial vent. Its elevation takes place in one or both 

 of two modes, viz. 1. By the accumulation of matter, protruded by re- 

 peated eruptions. 2. By elevation, en masse, from the expansion of the 



