United States or Lesotho ? Vote for the TOP Country of the Week !
KAINOZOIC OR TERTIARY: Pleistocene and Recent. Pliocene. Miocene. Oligocene. Eocene. MESOZOIC OR SECONDARY: Cretaceous. Jurassic. Triassic. PALAEOZOIC OR PRIMARY: Permian. Carboniferous. Devonian or old Red Sandstone. Silurian. Ordovician. Cambrian. A VILLAGE BUILT ON PILES IN A SWISS LAKE. Restored by Dr. Works of Art in Danish Peat-Mosses. Remains of three Periods of Vegetation in the Peat.
The periods we have already covered the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian form the Primary or Palaeozoic Era, to which the earlier Archaean rocks were prefixed as a barren and less interesting introduction. The stretch of time on which we now enter, at the close of the Permian, is the Secondary or Mesozoic Era.
Geographical provinces and zones may have been as distinctly marked in the Palaeozoic epoch as at present, and those seemingly sudden appearances of new genera and species, which we ascribe to new creation, may be simple results of migration. It may be so; it may be otherwise.
It is well known, for instance, that several species appear somewhat earlier in the palaeozoic beds of North America than in those of Europe; time having apparently been required for their migration from the American to the European seas.
Cassian beds, for example, Palaeozoic and Mesozoic forms are commingled, and, between the Cretaceous and the Eocene formations, there are similar transitional beds. On the other hand, in the middle of the Silurian series, extensive unconformity of the strata indicates the lapse of vast intervals of time between the deposit of successive beds, without any corresponding change in the Fauna.
Turning to the Invertebrata, Barrande asserts, a higher authority could not be named, that he is every day taught that, although palaeozoic animals can certainly be classed under existing groups, yet that at this ancient period the groups were not so distinctly separated from each other as they now are.
Both single species and whole groups of species last for very unequal periods; some groups, as we have seen, have endured from the earliest known dawn of life to the present day; some have disappeared before the close of the palaeozoic period. No fixed law seems to determine the length of time during which any single species or any single genus endures.
Some geologists, to avoid misapprehension, have introduced the term Palaeozoic for primary, from palaion, "ancient," and zoon, "an organic being," still retaining the terms secondary and tertiary; Mr.
The thickness of the strata belonging to each group amounts in some places to several thousand feet; and by dint of a careful examination of their geological position, and of those fossil, animal, and vegetable forms which are occasionally met with in some members of each series, it has at length been made clear that the older or Permian rocks are more connected with the Primary or Palaeozoic than with the Secondary or Mesozoic strata already described.
How do similar reasonings apply to the other great change of life that which took place at the end of the Palaeozoic period?
Word Of The Day