MACKIE ROCKS AND THEIR TEACHINGS. 



95 



state positively that it is more in quantity or volume than could have 

 been supplied from the disintegration of those primitive rocks. 



Let us go back as far in the series of fossiliferous rocks as we can ; 

 vre still find them, notwithstanding the subsequent alterations to which 

 they have been exposed, presenting similar features to the detrital 

 deposits of our seas and coasts. Even before we detect the traces of 

 organic remains, or the ripple-marks left on the sands of a lifeless shore, 

 we perceive the sedimentary nature of the stone in the disposition of 

 the scales of mica, and of the fine particles of the clayey slate • and we 

 look back almost instinctively for its source to the weather-beaten 

 coasts of the rugged granite- lands of a supposed untenanted globe. 



Perhaps, indeed, the records of still earlier stages of our world, and 

 still earlier creations than any we have yet discovered, have been 

 melted down by the fervent heat, or crystallized into those deep and 

 ancient rock-masses. 



Such speculations are not yet supported by any decisive proofs, but 

 they may not be the wildest nor most unreal. The doctrine of the 

 central heat of the globe may have to undergo great modifications, for 

 all we as yet know about it is deduced from a limited experience of the 

 variations of temperatures in mines and deep borings, while all indi- 

 cations of its internal fluidity rest wholly on some few intricate and obscure 

 astronomical and physical facts, with the calculations based upon them. 

 "We know as yet but very little of the influences which the subtle and 

 wonderful powers, electricity and crystallization, or which the various 

 chemical combinations constantly going on around and beneath us, are 

 capable of 65*00 ting. The vast granitic ridges are, however, commonly 

 regarded as the backbones of the earth, as the framework on which 

 the sedimentary crust has been formed-— and as such, for our present 

 purpose, we must accept them. Eut one thing is certain — we may 

 trace at least some, if not all, the materials of the sedimentary rocks 

 back to the granites ; but whence the constituent minerals of the latter 

 were derived we know not, nor whether the interior of our planet is 

 homogenous in its substance, or as diversified in its composition as that 

 coating of solid rocks in which it is enveloped. 



Let no one be dismayed at the difficulty of at first grasping the 

 marvellous details which geology presents in the formation, order, and 

 arrangements of the rocks. If we stand on the tower of a church, and 

 gaze around on a small town, we can make out the contiguous streets 



