67 



from these through long galleries and fissures of communication. Nor 

 have we in volcanic countries alone decisive evidence of the existence 

 of subterranean Cavities. No rock is exempt from Fissures : in thick 

 beds of limestone Fissures and Caverns are exceedingly abundant; and 

 the extent of these last is sometimes prodigious. Who has not heard 

 of the Grotto of Antiparos ? of the Caverns of Carinthia and Carniola, 

 the content of vi^hich amounts to some hundred thousand cubic feet ? 

 of the Kingston Cave recently explored near Michelstovi'n in Ireland ? 



To the frequency of Caverns and Openings, by whatever name de- 

 signated, I ascribe many of the inequalities which vary the surface of 

 the earth ; such openings, I conceive, produce phenomena sometimes 

 of Subsidence, sometimes of Elevation. I cannot entertain a doubt, 

 that many of the tilts and contortionsof strata usually ascribed to Sou- 

 levement, have been occasioned solely by want of adequate support. 



The Duchy of Finland exhibits an endless series of lakes filling up 

 the hollows of a granitic surface. Let me be allowed a similar series 

 of subterranean lakes occupying similar basins beneath the level of the 

 Baltic, an»l receiving, by means of Fissures extending up to the sum- 

 mits of the Scandinavian chain, a continual supply of water which has 

 no outlet ; in other words, let me be allowed the use of hydrostatic 

 pressure ; and without having recourse to central heat or secular re- 

 frigeration, I think I shall be able to account, without difficulty, not by 

 a general and uniform Rising, but by a number of unequal and partial 

 Risings, for the phenomena observed along the shores of the Baltic. 



Steam is often referred to as capable of producing the same result, 

 nor will I deny that it might do so under favourable circumstances ; 

 but I apprehend Steam rarely does act in nature under such circum- 

 stances ; for its existence depends on the access 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 become 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 sedimentary. 



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

 rocks are. My answer is, whatever geological speculators think proper 

 to call so. The late Professor Dugald Stewart cautioned us strongly, 

 though, alas ! in vain, to avoid the language 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 ex- 

 " amination, and will be best understood if the facts are given fairly, 

 " without any dependence on what should yet be considered as un- 

 " known ; this rule is very essential where the facts are in a certain 

 " degree complicated." 



In dealing out to rocks the ap|)ellation of igneous, some geologists 

 are more liberal than others. I have not time to enumerate the va- 

 rious rocks which enjoy this title, still less to investigate their respec- 

 tive claims to retain it. I will therefore content myself with observing, 

 that in the scantiest catalogue they are many in number, and con- 

 sequently, if ejected in a state of fusion, must have been ejected from 

 different reservoirs and cauldrons, not from a central cauldron. 



