RELATIVES OF THE OYSTER. 193 



Were, then, a mighty force below this surface to act 

 on certain points, and along certain lines, the wafer-patches 

 would be bent, broken, and have their edges often turned 

 up, so that those of the lower ones would stand in some 

 places over the higher ones that had been thus shattered. 

 And, now, were a mass of melted matter, which had lain 

 quietly beneath the lowest of the patches, to boil up, burst 

 forth in many places, to raise the wafers, piercing them, 

 finally hardening in fantastic shapes, and traversing over 

 the upheaved and fractured outside, there would be another 

 illustration of the state of the earth's surface. 



Such is the origin of granitic and similar rocks. 

 Boiling up, they gave rise to mountain ranges when they 

 could not pierce through the resistance ; but, when they 

 could, cooling, and remaining as magnificent crags and 

 summits. It is by following the broken edges or " out- 

 croppings " of the strata, carefully and intelligently, through 

 extensive tracts of country, that the series is disclosed from 

 the crystalline rocks, on which the first or lower stratum 

 rests, up to the last, lying immediately under the soil on 

 which we live, rear our edifices, and gather the produce of 

 our gardens and fields, (a) 



The astronomer may find good reasons for ascribing 

 the earth's form to the original fluidity of the mass, in 

 times long antecedent to the first introduction of living 

 beings into the planet ; but the geologist must be content 

 to regard the earliest monuments which it is his task to 

 interpret, as belonging to a period when the crust had 

 already acquired great solidity and thickness, probably as 

 great as it now possesses, and when volcanic rocks, not 

 essentially differing from those now produced, were formed 

 (a) "Adventures of an Oyster," pp. 56-58. 



