THE EARTH FORMED. 



greater at greater depths ; so that the entire mass of a 

 cool globe should be of a gravity infinitely exceeding 

 four and a half times the weight of water. The only al- 

 ternative supposition is, that the central materials are 

 greatly expanded or diffused by some means; and by 

 what means could they be so expanded but by heat ! In- 

 deed, the existence of this central heat, a residuum of 

 that which kept all matter in a vaporiform chaos at first, 

 is amongst the most solid discoveries of modern science,* 

 and the support which it gives to Herschel's explanation 

 of the formation of worlds is most important. We shall 

 hereafter see what appear* to be traces of an operation of 

 this heat upon the surface of the earth in very remote 

 times ; an effect, however, which has long passed entirely 

 away. The central heat has, for ages, reached a fixed 

 point, at which it will probably remain for ever, as the 

 non-conducting quality of the cool crust absolutely pre- 

 vents it from suffering any diminution. 



THE EARTH FORMED — ERA OF THE PRIMARY 

 ROCKS. 



Although the earth has not been actually penetrated 

 to a greater depth than three thousand feet, the nature 

 of its substance can, in many instances, be inferred for 

 the depth of many miles by other means of observation. 

 We see a mountain composed of a particular substance, 

 with strata, or beds of other rock, lying against its sloped 

 sides : we, of course, infer that the substance of the 

 mountain dips away under the strata which we see lying 

 against it. Suppose that we walk away from the moun- 

 tain across the turned up edges of the stratified rocks, and 

 that for many miles we continue to pass over other stra- 

 tified rocks, all disposed in the same way, till by and bye 

 we come to a place where we begin to cross the opposite 

 edges of the same beds ; after which we pass over these 

 rocks all in reverse order, till we come to another exten- 

 sive mountain composed of similar material to the first, 

 and shelving away under the strata in the same way. We 

 should then infer, that the stratified rocks occupied a ba- 



* The researches on this subject were conducted chiefly by the 

 late Baron Fourier, perpetual secretary to the Academy of Sciences 

 of Paris See his Tkeorie Analytique de la Chaleur, 1822. 



