46 VOLCANIC ROCKS, 



stability. Very different are the feelings of those whose lot 

 is cast near the foci of volcanic eruptions ; to them the earth 

 affords no stable resting place, but during the paroxysms of 

 volcanic activity, reels to and fro, and vibrates beneath their 

 feet; overthroM^ing cities, yavsrning with dreadful chasms, 

 converting seas into dry lands, and dry lands into seas. (See 

 Lyell's Geology, vol. i. passim.) 



To the inhabitants of such districts we speak a language 

 which they fully comprehend, when we describe the crust 

 of the globe as floating on an internal nucleus of molten 

 elements; they have seen these molten elements burst forth 

 in liquid streams of lava; they have felt the earth beneath 

 them quivering and roUing, as if upon the billows of a sub- 

 terranean sea; they have seen mountains raised and valleys 

 depressed almost in an instant of time ; they can duly ap- 

 preciate, from sensible experience, the force of the terms in 

 which geologists describe the tremulous throes, and convul- 

 sive agitations of the earth ; during the passage of its strata 

 from the bottom of the seas, in which they received their 

 origin, to the plains and mountains in which they find their 

 present place of rest. 



We see that the streams of earthy matter, which issue 

 in a state of fusion from active volcanos, are spread around 

 their craters in sheets of many kinds of lava; some of these 

 so much resemble beds of basalt, and various trap rocks, 

 that occur in districts remote from any existing volcanic 

 vent as to render it probable that the latter also have been 

 poured forth from the interior of the earth. We farther find 

 the rocks adjacent to volcanic craters, intersected by rents 

 and fissures, which have been filled with injections of more 

 recent lava, forming transverse walls or dikes. Similar 

 dikes occur not only in districts occupied by basalt and 

 trap rocks, at a distance from the site of any modern 

 volcanic activity; but also in strata of every formation, 

 from the most ancient primary, to the most recent tertiary 

 (see Plate 1. section f 1— f 8. h 1— h 2. i 1— i 5:) and as 



