Ignecms Rocks viewed as Agents of Elevation. 223 



risings, for the phenomena observed along the shores of the 

 Baltic. ^.''f'^' *'^ ■ 



Steam is often referred to as capable of producing the same 

 result, nor will I deny that it might do so under favourable cir- 

 cumstances ; but I apprehend steam rarely does act in nature 

 under such circumstances ; for its existence depends on the ac- 

 cess of heat, and its force on close confinement, contingencies 

 not very likely to occur in the porous and fissured strata of the 

 earth. Any of the various gases, if compressed, might also be- 

 come agents of elevation, but only under the same conditions as 

 steam. 



;: I have reserved for the last the popular theory which accounts 

 for elevation by the forcible inroad of igneous rocks into sedi- 

 inentary. 



To put this theory to the test, it is natural to inquire, what 

 igneous rocks are ? My answer is, whatever geological specula- 

 tors think proper to call so. The late Professor Dugald Stewart 

 cautioned us strongly, though, alas ! in vain, to avoid the lan- 

 guage of theory. " Appearances," he observes, " should always 

 be described in terms which involve no opinion as to their causes. 

 These are the objects of separate examination, and will be best 

 understood if the facts are given fairly, without any dependence 

 on what should yet be considered as unknown ; this rule is very 

 essential where the facts are in a certain degree complicated." 



In dealing out to rocks the appellation of igneous^ some geo- 

 logists are more liberal than others. I have not time to enume- 

 rate the various rocks which enjoy this title, still less to investi- 

 gate their respective claims to retain it. I will therefore content 

 myself with observing, that in the scantiest catalogue they are 

 many in number, and consequently, if ejected in a state of fu- 

 sion, must have been ejected from different reservoirs and cauld- 

 rons, not from a central cauldron. 



That any rock whatever was originally igneous, is a gratui- 

 tous assumption. Lavas themselves may be, and probably are, 

 in very many cases, rocks not originally igneous, but rocks 

 which have been exposed at one time or other to the action of 

 fire. 



Granite is one of the rocks most usually considered as an 

 agent in elevation , for what reason I am at a loss to discover. 



q2 



