382 
CONCLUDING REMARKS. 
[Ch. XXVI, 
cessive periods, has extended over a subterranean space equal 
at least in area to the present European continent, and often 
through a portion of the earth's crust 4000 feet or more in 
thickness. 
The principal effect of these volcanic operations in the nether 
regions, during the tertiary periods, or since the existing species 
began to flourish, has been to heave up to the surface hypogene 
formations of an age anterior to the carboniferous. We 
imagine that the repetition of another series of movements, of 
equal violence, might upraise the plutonic and metamorphic 
rocks of many of the secondary periods ; and if the same force 
should still continue to act, the next convulsions might bring 
up the tertiary and recent hypogene rocks, by which time we 
imagine that nearly all the sedimentary strata now in sight 
would either have been destroyed by the action of water, or 
would have assumed the metamorphic structure, or would have 
been melted down into plutonic and volcanic rocks. 
At the close of this chapter the reader will find a table of 
the chronological relations of the principal divisions of rocks 
according to the views above set forth. The sketch is con- 
fessedly imperfect, but it will elucidate our theory of the con- 
nexion which may exist between the hypogene rocks of different 
periods,, and the alluvial, volcanic, and sedimentary formations. 
A second table is added, containing the names of some of the 
principal groups of sedimentary strata mentioned in this work, 
arranged in their order of superposition. 
Concluding Remarks.* — In our history of the progress of 
geology, in the first volume, we stated that the opinion 
originally promulgated by Hutton, ' that the strata called 
primitive were mere altered sedimentary rocks,' was vehe- 
mently opposed for a time, the main objection to the theory 
being its supposed tendency to promote a belief in the past 
eternity of our planet. Previously the absence of animal 
and vegetable remains in the so-called primitive strata, had 
been appealed to, as proving that there had been a period when 
the planet was uninhabited by living beings, and when, as was 
