A Brief Sketch of the Geology of the West Indies. 159 



preserving the uniformity of composition of the atmosphere. In the 

 earth we witness influences of the like kind, as it were opposed to 

 each other, and producing opposite effects. Water, in its operation, 

 aided by air, may be considered as destructive, wearing away rocks 

 and mountains, and carrying their comminuted parts to lower levels, 

 and oven into the sea, to be buried in its depths. Fire may be con- 

 sidered as restorative ; acting below the surface, it melts and also 

 consolidates, according to its degree of intensity, tending to reproduce 

 crystalline rocks in one instance, and stratified in the other. Even 

 when it appears most eminently to act according to our ordinary 

 notions of its operation as a devastating and destroying agent, for 

 example, in the eruption of a volcano, the ashes which are discharged 

 into the atmosphere, and are widely scattered by the winds, even 

 when they fall on the adjoining countries, may help to supply the 

 place of the old surface-materials, carried away by streams and floods, 

 and to renovate the soil with new elements of fertility. And acting 

 in another form and manner, the same power which occasions volcanic 

 eruptions appears to be productive of another effect, viz., the gra- 

 dual elevation of the bed of the sea, tending to the formation of new 

 land, of which we seem to have examples in the extension of certain 

 coasts, and the appearance of rocks and dry land above the waves, 

 preceded by a gradual diminution of the water over the spots where 

 these remarkable phenomena occur. 



Of most of the geological changes alluded to in the preceding re- 

 marks, the West Indies afford well marked instances. 



From the continent of America are to be seen vast rivers flowing 

 into the sea, turbid with the detritus of the country through which 

 they have descended in a course of thousands of miles, and discolour- 

 ing and freshening the waters with which they mix at an extraor- 

 dinary distance from land. Between their mouths on the coasts and 

 their rapids in the boundary hills of the interior, immense level, or 

 almost level tracts occur, — ^marsh, morass, and sandbank, neither 

 land nor water, covered chiefly with aquatic plants,— -tracts formed by 

 deposits from the great rivers, and commonly of materials somewhat 

 coarser and heavier than those which are longer suspended and are 

 carried out into the sea in consequence of their greater fineness. 



In many of the islands not only are there rocks to be seen evi- 

 dently of volcanic origin — columnar basalt, trachite, and many varieties 

 of tufa, but also craters from whence eruptions have taken place, 

 and in which the fires are hardly yet extinct that once acted, as is 

 indicated by the hot steams and exhalations still proceeding from 

 them. 



Moreover, in some of these islands, rocks of volcanic origin,^crys- 

 talline in their structure, and totally destitute of organic remains, are 

 associated with others of a perfectly different character, stratified and 

 abounding in organic remains, — ^various species of sea shells and of 

 coral ; and it is worthy of notice, that, in one of the instances in 



