Comparison with 1872 |
|
of time, all included within this same glacial period. Yet it may be doubted whether
in any quarter of the world, sedimentary deposits,
including
fossil
remains
,
remains
,
1859 1860 1866 1872 | remains, 1861 |
remains,
1869 |
have gone on accumulating within the same area during the whole of this period. It is not, for instance, probable that sediment was deposited during the whole of the glacial period near the mouth of the Mississippi, within that limit of depth at which marine animals can flourish;
for we know what
vast
geographical changes occurred in other parts of America during this space of time. When such beds as were deposited in shallow water near the mouth of the Mississippi during some part of the glacial period shall have been upraised, organic remains will probably first appear and disappear at different levels, owing to the migration
of species and to geographical changes. And in the distant future, a geologist
examining these beds, might
be tempted to conclude that the average duration of life of the embedded fossils had been less than that of the glacial period, instead of having been really far greater, that is
extending from before the glacial epoch to the present day. |
|
In order to get a perfect gradation between two forms in the upper and lower parts of the same formation, the deposit
must must 1859 1860 1861 1872 | will 1866 1869 |
have
gone on continuously accumulating during a gone on continuously accumulating during a 1872 |
gone on accumulating for a very 1859 1860 1861 |
to go on continuously accumulating during a very 1866 1869 |
long period,
sufficient sufficient 1872 |
in order to have given sufficient time 1859 1860 |
so that there may have been time sufficient 1861 |
so that there may be time sufficient 1866 1869 |
for the slow process of variation;
hence the deposit
must must 1872 |
will generally have to 1859 1860 1861 |
will have to 1866 1869 |
be a very thick one; and the species undergoing
change must have lived in change must have lived in 1872 |
modification will have had to live on 1859 1860 1861 |
modification will have to live in 1866 |
change will have to live in 1869 |
the same area
throughout
the the 1872 | this 1859 1860 1861 1866 1869 |
whole time. But we have seen that a thick fossiliferous formation
can only be accumulated
during a period of subsidence; and to keep the depth approximately the same, which is necessary in order to enable
the same species to
live on the same space, the supply of sediment must
|
of time, all included within this same glacial period. Yet it may be doubted
whether, whether, 1866 1869 1872 | whether 1859 1860 1861 |
in any quarter of the world, sedimentary deposits,
including
including
1859 1860 1866 1869 1872 | including 1861 |
fossil
fossil
1859 1860 1866 1869 1872 | fossil 1861 |
remains,
remains,
1869 |
remains
,
1859 1860 1866 1872 | remains, 1861 |
have gone on accumulating within the same area during the whole of this period. It is not, for instance, probable that sediment was deposited during the whole of the glacial period near the mouth of the Mississippi, within that limit of depth at which marine animals can
best flourish: best flourish: 1869 1872 | flourish; 1859 1860 1861 1866 |
for we know
that that 1869 1872 | what 1859 1860 1861 1866 |
great great 1869 1872 | vast 1859 1860 1861 1866 |
geographical changes occurred in other parts of America during this space of time. When such beds as were deposited in shallow water near the mouth of the Mississippi during some part of the glacial period shall have been upraised, organic remains will probably first appear and disappear at different levels, owing to the
migrations migrations 1869 1872 | migration 1859 1860 1861 1866 |
of species and to geographical changes. And in the distant future, a
geologist, geologist, 1866 1869 1872 | geologist 1859 1860 1861 |
examining these beds,
would would 1866 1869 1872 | might 1859 1860 1861 |
be tempted to conclude that the average duration of life of the embedded fossils had been less than that of the glacial period, instead of having been really far greater, that
is, is, 1861 1866 1869 1872 | is 1859 1860 |
extending from before the glacial epoch to the present day. |
|
In order to get a perfect gradation between two forms in the upper and lower parts of the same formation, the deposit
will will 1866 1869 | must 1859 1860 1861 1872 |
have
to go on continuously accumulating during a very to go on continuously accumulating during a very 1866 1869 |
gone on accumulating for a very 1859 1860 1861 |
gone on continuously accumulating during a 1872 |
long period,
so that there may be time sufficient so that there may be time sufficient 1866 1869 |
in order to have given sufficient time 1859 1860 |
so that there may have been time sufficient 1861 |
sufficient 1872 |
for the slow process of
modification; modification; 1869 1872 | variation; 1859 1860 1861 1866 |
hence the deposit
will have to will have to 1866 1869 |
will generally have to 1859 1860 1861 |
must 1872 |
be a very thick one; and the species
undergoing undergoing 1859 1860 1861 1869 1872 | under- going 1866 |
change will have to live in change will have to live in 1869 |
modification will have had to live on 1859 1860 1861 |
modification will have to live in 1866 |
change must have lived in 1872 |
the same
district district 1866 1869 1872 | area 1859 1860 1861 |
throughout
this this 1859 1860 1861 1866 1869 | the 1872 |
whole time. But we have seen that a thick
formation, formation, 1866 1869 1872 |
fossiliferous formation 1859 1860 |
formation, fossiliferous throughout its thickness, 1861 |
fossiliferous throughout its entire thickness, can accumulate only fossiliferous throughout its entire thickness, can accumulate only 1869 1872 |
can only be accumulated 1859 1860 1861 |
fossiliferous throughout its thickness, can accumulate only 1866 |
during a period of subsidence; and to keep the depth approximately the same, which is necessary
that that 1861 1866 1869 1872 |
in order to enable 1859 1860 |
the same
marine species may marine species may 1866 1869 1872 |
species to 1859 1860 |
species may 1861 |
live on the same space, the supply of sediment must
|