| → stratum 1859 1860 1861 1866 1872 |
| or Cambrian stratum 1869 |
|
| → yet quite unknown, periods of time, 1859 1860 1861 1866 |
| periods 1869 1872 |
|
| ↑ 4 blocks not present in 1859 1860 1861 1866; present in 1869 1872 |
| Here we encounter a formidable objection; for it seems doubtful whether the earth
in a fit state for the habitation of living creatures
has lasted long enough.
Sir W. Thompson concludes that the consolidation of the crust can hardly have occurred less than 20 or more than 400 million years ago, but probably not less than 98 or more than 200 million years.
These very wide limits show how doubtful the data are; and other elements may have to
be introduced into the problem.
Mr. Croll estimates that about 60 million years have elapsed since the Cambrian period, but this, judging from the small amount of organic change since the commencement of the Glacial epoch, seems
a very short time for the many and great mutations of life, which have certainly occurred since the Cambrian formation; and the previous 140 million years can hardly be considered as sufficient for the development of the varied forms of life which certainly
existed towards
the close of the
Cambrian period.
|
|
| ↑ 1 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| It is, however, probable, as Sir William Thompson insists, that the world at a very early period was subjected to more rapid and violent changes in its physical conditions than those now occurring; and such changes would have tended to induce changes at a corresponding rate in the organisms which then existed.
|
|
| → records of these vast primordial periods, 1859 1860 1861 |
| richly fossiliferous records of these vast primordial periods, 1866 |
| rich fossiliferous deposits belonging to these assumed earliest periods, 1869 |
| rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, 1872 |
|
| → of the most 1859 1860 1861 |
| OMIT 1866 1869 1872 |
|
| → are 1859 1860 1861 |
| were until recently 1866 1869 1872 |
|
| → M. Barrande has lately 1859 1860 1861 |
| M. Barrande not long ago 1866 |
| Not long ago M. Barrande 1869 |
| Not very long ago M. Barrande 1872 |
|
| → to the Silurian system, 1859 1860 1861 1866 |
| OMIT 1869 1872 |
|
| → species. 1859 1860 1861 1866 |
| species beneath the old Silurian system. 1869 |
| species, beneath the then known Silurian system; and now, still lower down in the Lower Cambrian formation, Mr. Hicks has found in South Wales beds rich in trilobites, and containing various molluscs and annelids. 1872 |
|
| → life have 1859 1860 1861 |
| several forms have 1866 |
| several forms have also 1869 |
|
| → in the Longmynd beds 1859 |
| in the Longmynd beds, 1860 1861 1866 |
| OMIT 1869 |
|
| → zone. 1859 1860 1861 1866 |
| zone in the Longmynd group, now divided into two stages, and constituting the Lower Cambrian system. 1869 |
|
| → the difficulty of understanding the absence of vast piles of fossiliferous strata, which on my theory no doubt were somewhere accumulated before the Silurian epoch, is very great. 1859 1860 1861 |
| now within the last year the great discovery of the Eozoon in the Laurentian formation of Canada has been made; and after reading Dr. Carpenter's description of this remarkable fossil, it is impossible to feel any doubt regarding its organic nature. 1866 |
|
| → If these 1859 1860 1861 |
| If the 1866 |
| It does not seem probable that the 1869 1872 |
|
| → obliterated 1859 1860 1861 |
| if their fossils had been wholly obliterated 1866 |
| that their fossils have been wholly obliterated 1869 1872 |
|
| → we ought to find 1859 1860 1861 |
| we ought to have found 1866 |
| for if this had been the case we should have found 1869 1872 |
|
| → ought to be very generally 1859 1860 1861 |
| ought to have existed almost always 1866 |
| would always have existed 1869 1872 |
|
