MACKIE llOCKS 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 ; 
we 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 effecting. 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. But 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 difiiculty of at fii'st 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 
