28 



THE EARTH FORMED. 



settlement of the earth in its present form. They are in 

 deed of an order of events which we see going on, tinder 

 the agency of more or less intelligible causes, even down 

 to the present day. We may therefore consider them ge- 

 nerally as comparatively recent transactions. Abstracting 

 them from the investigations before us, we arrive at the 

 idea of the earth in its first condition as a globe of its pre- 

 sent size — namely, as a mass, externally at least, consist- 

 ing of the crystalline kind of rock, with the waters of the 

 present seas and the present, atmosphere around it, though 

 these were probably in considerably different conditions, 

 both as to temperature and their constituent materials 

 from what they now are. We are thus to presume that 

 that crystalline texture of rock which we see exemplified 

 in granite is the condition into which the great bulk of 

 the solids of our earth were agglomerated directly from the 

 nebulous or vaporiform state. It is a condition eminently 

 of combination, for such rock is invariably composed of 

 two or more of four substances — silica, mica, quartz and 

 hornblende— which associate in it in the form of grains or 

 crystals, and which are themselves each composed of a 

 group of the simple or elementary substances. 



Judging from the results and from still remaining con- 

 ditions, we must suppose that the heat retained in the in- 

 terior of the globe was more intense, or had greater free- 

 dom to act in some place3 than in others. These became 

 the scenes of volcanic operations, and in time marked 

 their situations by the extrusion of traps and basalts from 

 below — namely, rocks composed of the crystalline matter 

 fused by intense heat, and developed on the surface in 

 various conditions, according to the partiular circumstan- 

 ces under which it was sent up ; some, for example, be- 

 ing thrown up under water, and some in the open air, 

 which conditions are found to have made considerable 

 difference in its texture and appearance. The great stores 

 01 subterranean heat also served an important purpose in 

 the formation of the aqueous rocks. These rocks might, 

 according to Sir JohnHerschel, become subject to heat in 

 the following manner ; — While the surface of a particu- 

 lar mass of rock forms the bed of the sea, the heat is kept 

 at a certain distance from that surface by the contact ol 

 the water ; philosophically speaking, it radiates away the 

 heat into the sea, and (to resort to common language) is 

 Pooled a good way down. But when new sediment set- 



