PRINCIPLES OF CLASSIFICATION. 
139 
less abrupt, yet the entire series of records appears to the 
geologists now living far more fragmentary and defective 
than it seemed to their predecessors half a century ago. 
The earlier inquirers, as often as they encountered a break 
in the regular sequence of formatioxis, connected it theoretic¬ 
ally with a sudden and violent catastrophe, w^hich had put 
an end to the regular course of events that had been going 
on uninterruptedly for ages, annihilating at the same time all 
or nearly all the organic beings which had previously flour¬ 
ished, after which, order being re-established, a new series of 
events was initiated. In proportion as our faith in these 
views grows weaker, and the phenomena of the organic or 
inorganic world presented to us by geology seem explicable 
on the hypothesis of gradual and insensiWe changes, varied 
only by occasional convulsions, on a scale comparable to that 
witnessed in historical times; and in proportion as it is 
thought possible that former fluctuations in the organic world 
may be due to the indeflnite modifiability of species without 
the necessity of assuming new and independent acts of cre¬ 
ation, the number and magnitude of the gaps which still re¬ 
main, or the extreme imperfection of the record, become more 
and more striking, and what we possess of the ancient annals 
of the earth’s history appears as nothing when contrasted 
with that which has been lost. 
When we examine a large area such as Europe, the aver¬ 
age as well as the extreme height above the sea attained by 
the older formations is usually found to exceed that reached 
by the more modern ones, the primary or palaeozoic rising 
higher than the secondary, and these in their turn than the 
tertiary; while in reference to the three divisions of the ter¬ 
tiary, the lowest or Eocene group attains a higher summit- 
level than the Miocene, and these again a greater height 
than the Pliocene formations. Lastly, the post-tertiary de¬ 
posits, such, at least, as are of marine origin, are most com¬ 
monly restricted to much more moderate elevations above 
the sea-level than the tertiary strata. 
It is also observed that strata, in proportion as they are 
of newer date, bear the nearest resemblance in mineral char¬ 
acter to those which are now in the progress of formation in 
seas or lakes, the newest of all consisting principally of soft 
mud or loose sand, in some places full of shells, corals, or 
other organic bodies, animal or vegetable, in others wholly 
devoid of such remains. The farther we recede from the 
present time, and the higher the antiquity of the formations 
which we examine, the greater are the changes which the 
sedimentary deposits have undergone. Time, as I have ex- 
