Origin of Species Variorum

→ 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

→ 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

→ will have to 1866 1869

will generally have to 1859 1860 1861

must 1872

→ 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

→ formation, 1866 1869 1872

fossiliferous formation 1859 1860

formation, fossiliferous throughout its thickness, 1861

→ 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

→ that 1861 1866 1869 1872

in order to enable 1859 1860

→ marine species may 1866 1869 1872

species to 1859 1860

species may 1861

of time, all included within this same glacial period. Yet it may be doubted

whether

whether,

in any quarter of the world, sedimentary deposits,

including

including

fossil

fossil

remains ,

remains,

remains,

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;

best flourish:

for we know

what

that

vast

great

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

migrations

of species and to geographical changes. And in the distant future, a

geologist

geologist,

examining these beds,

might

would

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

will

have →to go on continuously accumulating during a very long period, →so that there may be time sufficient for the slow process of

variation;

modification;

hence the deposit →will have to be a very thick one; and the species

under- going

undergoing

→change will have to live in the same

area

district

throughout

the

this

whole time. But we have seen that a thick →formation, →fossiliferous throughout its entire thickness, can accumulate only during a period of subsidence; and to keep the depth approximately the same, which is necessary →that the same →marine species may live on the same space, the supply of sediment must