546 



THE GEOLOGIST. 



unequal contractions of its different parts ; and in a cooling globe compound 

 gases could not be expected to produce any decided mechanical effect, at least 

 without materially altering the composition of the atmosphere. But, apart 

 from these causes, the transition of the igneous rocks from a fluid to a solid 

 state would be attended with occasional paroxysmal movement and change. 

 Being dependent on hydrostatic conditions for stability, the different parts of 

 the earth's crust must extend into the greater reservoir of lava to a depth in 

 some measure proportionate to the elevation above its surface. Continents 

 must rest on solid foundations far deeper than those which supported the body 

 of the ocean ; and the violence which subterranean forces manifested in several 

 islands might be ascribed in part to the weakness of the barriers which re- 

 strained them. Inequalities in the solid envelope of our globe were indicated 

 with some certainty by local forces of gravity. The anomalous character of 

 the vibrations of the pendulum, when applied in some places, justified the con- 

 clusion that the invisible side of the earth's crust contained the greatest 

 irregularities, and that our continental tracts of land rest on the bases of 

 gigantic subterranean mountains, whose tops might be depressed even three 

 or four hundred miles below the mean level of the solidified matter. The 

 accumulations of solid matter on the internal mountains must ultimately be 

 crushed by the strain which their augmented size occasioned; a mighty 

 avalanche of rock would then tumble to the thinner part of the earth's crust. 

 Regarding these masses as the cause of earthquakes, they might account for 

 the instantaneous manner in which shocks of earthquakes occurred, their 

 extreme violence, and destructive character near the coasts of continents and 

 on adjacent islands, while they were almost imperceptible in the interior of 

 continents. It was probable that the ascending movements of silica, and 

 perhaps of other isolated matter, might serve to bring the heavy metallic 

 deposits from the central to the superficial regions of our planet ; and the 

 general occurrence of gold in auriferous quartz-rock might thus admit of 

 plausible explanation. 



THE FORMATION OF LAND. 



By the Rev. C. R. Gordon, M.A., F.R.S. 



The Rev. C. R. Gordon, M.A., F.R.S., proceeded to say that the solid parts 

 of the globe are in general composed of sand, gravel, argillaceous and cal- 

 careous strata, or of the various compositions of these with other substances. 

 Calcareous bodies belong to the sea, and are formed in it. There are only two 

 ways by which porous or spongy bodies can be consolidated, either by conge- 

 lation or attrition. To procure solidity, it must be brought about by inducing 

 fluidity, either immediately by the action of heat, or directly by the operation 

 of a solution. Thus, fire and water may be considered as the general agents in 

 this operation. The strata formed at 'the bottom of the sea are to be con- 

 sidered, therefore, as having been consolidated either by aqueous solution and 

 crystallization, or by the effect of heat and fusion. We have strata consolidated 

 by calcareous spar. We have strata made solid by fluor, a substance not 

 soluble, so far as is known, by water. We have strata consolidated with sul- 

 phureous and bituminous substances, which do not correspond to the solution 

 by water. We have strata consolidated with siliceous matter, in a state totally 

 different from that under which it has been observed, on certain occasions, to 

 be deposited by water, some consolidated by felspar, a substance indissoluble 

 m water, some also consolidated by almost all the various metallic substances, 



