ERA OF THE PRIMARY ROCKS. 



27 



sin formed by the rock of these two mountains, and by 

 calculating the thickness right through these strata, could 

 be able to say to what depth the rock of the mountain 

 extended below. By such means, the kind of rock exist- 

 ing many miles below the surface can often be inferred 

 with considerable confidence. 



The interior of the globe has now been inspected in this 

 way in many places, and a tolerably distinct notion of its 

 general arrangements has consequently been arrived at. 

 It appears that the basis rock of the earth, as it may be 

 called, is of hard texture, and crystalline in its constitu- 

 tion. Of this rock granite may be said to be the type, 

 though it runs into many varieties. Over this, except 

 in the comparitively few places where it projects above 

 the general level in mountains, other rocks are disposed 

 in sheets or strata, with the appearance of having been 

 deposited originally from water ; but these last rocks have 

 nowhere been allowed to rest in their original arrange- 

 ment. Uneasy movements from below have broken them 

 up in great inclined masses, while in many cases there 

 has been projected through the rents rocky matter more 

 or less resembling the great inferior crystalline mass. 

 This rocky matter must have been in a state of fusion at 

 the time of its projection, for it is often found to have run 

 into and filled up lateral chinks in these rents. There are 

 even instances where it has been rent again, and a newer 

 melted matter of the same character sent through the ope- 

 ning. Finally, in the crust as thus arranged there are, in 

 many places, chinks containing veins of metal. Thus, 

 there is first a great inferior mass, composed of crystalline 

 rock, and probably resting immediately on the fused and 

 expanded matter of the interior : next, layer or strata of 

 aqueous origin ; next, irregular masses of melted inferior 

 rock that have been sent up volcanically and confusedly 

 at various times amongst the aqueous rocks, breaking up 

 these into masses, and tossing them out of their original 

 levels. This is an outline of the arrangements of the crust 

 of the earth, as far as we can observe it. It is, at first 

 sight, a most confused scene; but after some careful ob- 

 servation, we readily detect in it a regularity and order 

 from which much instruction in the history of our globe 

 is to be derived. 



The deposition of the aqueous rocks, and the projection 

 of the volcan ic, have unquestionably taken place since the 



