368 Analysis of Scientific Books. 



author's pardon for substituting such vulgar language ; and, 

 therefore the eruption will be invisible, till the erupted matters are 

 elevated above the surface of the water; while " the mineral and 

 saline compounds which, in greater or less quantity, always ac- 

 company the aqueous vapour evolved from a volcanic vent, will, 

 on the condensation of this vapour, mingle with the waters of the 

 ocean, and add to the ingredients of the same nature with which 

 it is impregnated. " We think it extremely probable. 



With equal accuracy it is concluded, that some of the frag- 

 ments will accumulate round the vent and form a cone, while 

 those which are " scattered to any height by the gaseous explo- 

 sions, and particularly the lightest and finest of the fragmentary 

 matters," will render the ocean muddy, or " turbid," and finally 

 be deposited so as to form " sedimentary strata ; " and thus, as 

 pumice floats on water, it may be driven by winds and currents, 

 and deposited at distant points. Also, if the waters are impreg- 

 nated with calcareous matter, these tufas will have a calcareous 

 cement ; and those which form a thick paste, will produce a tufa- 

 ceous stone more readily than the more dispersed floating dust. 



As to the subaqueous lavas, "they will spread laterally beneath 

 the cover of a scoriform envelope, with a rapidity and to an extent 

 proportioned to the propulsive force, their fluidity, and the per- 

 manence of that fluidity, and the accidents of level in the sur- 

 rounding surfaces." The author also considers, that submarine 

 lavas will preserve their fluidity longer than subaerial ones, in 

 consequence of the superincumbent weight of water preventing 

 the escape of the interior waters, which he has already proved to 

 i>e the cause of its fluidity; and, showing that the extension of 

 such beds of lava must be proportioned to the depth of ocean 

 above, he thus accounts for the great extent of the generality of 

 ilotz-tr.ap formations. This pressure explains two other phe- 

 nomena occurring in these rocks ; first, why they possess no air 

 vesicles ; and, secondly, why they do possess them, as in the case 

 of the amygdaloids. The first consequence arises from the " in- 

 stantaneous consolidation " of the surface of the lava, aided by 

 the superincumbent pressure, preventing the escape of the vapour 

 "bubbles " by the ascending force of their inferior specific gravity," 

 a great cause of " perplexity to geologists." In the second con- 

 sequence, vesicles must be expected in the interior of the rock 

 lt whenever its liquidity was sufficient ta permit the agglomeration 

 of the vapour into parcels ; the extreme tension of the elastic 

 fluid causing the expansion of the bubbles as the lava flows on," 

 while, from the consolidation and pressure, as before, few can 

 escape by " rising outwardly." 



The author notices, of course, how volcanic cones, at first 

 merely .eruptive under the sea, may be raised above it by the 



