358 
that we can say from these discoveries is, that the lowest rocks 
yet known to popular geology are sedimentary. If by the 
leadings of the highest note in the world, we go down to 
those sand-rocks seen in the pebbles of Laurentian conglo- 
merate, and ask for the character of the rocks on which their 
sand was first laid down, we have no reply. We are not told 
that the foundation is granitic, nor are we told that it is not so. 
Our conscious ignorance here is, perhaps, our surest know- 
ledge. We know that we do not know — that is all. 
Hutton represents that host of speculators who still go 
down to the centre of the earth, and see all on fire. Because 
veins of superincumbent rock were full of granite that looked 
as if it had been melted and injected from below, he imagined, 
as we have seen, that the conclusion was irresistibly estab- 
lished that the basis of all the strata of the earth's crust was 
cooled lava, or molten rock cooled down and crystallized under 
great superincumbent pressure. It is most instructive to see how 
the very best authorities were led astray by this unfounded 
notion. As an illustration of this, though the author is one 
who discourages conjecture (at least in words), we find in Page s 
Advanced Text-Book (1856) the statement that the variable 
temperature of the crust of the earth descends to from sixty 
to ninety feet, “but at this limit it is stationary." Then he 
says, “that downwards from this invariable stratum, the tem- 
perature increases at the ratio of one degree for every fifty 01 
fifty-five feet, and at this rate a temperature would soon be 
reached sufficient to keep in fusion the most refractory rock 
substances " !* At the depth of twenty-five miles, his estimate 
is 2,400° Fahrenheit ! This is surely hot enough for the most 
fiery philosopher. To give another instance. "Whewell says, 
in the second edition of his admirable history, legal ding 
Hutton's theory, (which, how ever, he admits was “premature,") 
“ that many of its boldest hypotheses and generalizations have 
become a part of the general creed of geologists; and its 
publication is, perhaps, the greatest event which has yet 
occurred in the progress of Physical Geology." t These words 
were published in 1857 ; and in 1865 the very foundations oi 
Hutton's theory were seen by all informed men to be false. 
Playfair, Hr. Hutton's great illustrator, says, The power of 
the same subterranean heat which consolidated and mineral- 
ized the strata at the bottom of the sea, has since raised them 
up to the height at which they are now placed, and has given 
them the various inclinations to the horizon which they are 
found actually to possess." J This is just what the very best 
* Page’s Advanced Text-Book, p. 15. f Whew ell’s Hist., voL iii. p. oOo. 
X Playfair’s Illustrations, edition 1802, p. 55. 
