Its upheaval above the great sea which submerged all the north-west of the Indian peninsula long after the Himalaya had massed itself as a formidable mountain chain, belongs to a comparatively recent geologic period, and the same thrust upwards of vast masses of cretaceous limestone has disturbed the overlying recent beds of shale and clays with very similar results to those which have left so marked an impress on the Baluch frontier.
Geologically the anthracite and bituminous coals mainly belong to the same formation, the Carboniferous, and this is especially true of the better qualities; though it is stated by the United States Geological Survey that the geQlogic age of the coal beds ranges from Carboniferous in the Appalachian and Mississippi Valley provinces to Miocene (Tertiary) on the Pacific coast, and that the quality of the coal varies only to a very uncertain degree with the geologic age.
The theory of past migrations from continent to continent, suggested by Cuvier to explain the replacement of the animal life which had become extinct through sudden geologic changes, was prophetic of one of the chief features of modern method - namely, the tracing of migrations.
Such a drying up has been in progress during long geologic ages, but doubt exists as to its practical importance at the present time.
The geologic record is, as perhaps is to be expected, exceedingly poor, except as regards the calcareous Siphonales, which are well represented at various horizons, from the Silurian to the Tertiary; even the Diatomaceae, which are found in great quantities in the Tertiary deposits, do not occur at all earlier than the chalk.
This principle has been demonstrated recently among Tertiary rhinoceroses and titanotheres, in which remains of four or five genetic series in the same geologic deposits have been discovered.
In the order of decreasing geologic age and maturity.
Waagen's law of mutation, or the appearance of new parts or organs so gradually that they can be perceived only by following them through successive geologic time stages, appears to be directly contradictory to the saltation principle; it is certainly one of the most firmly established principles of palaeontology, and it constitutes the contribution par excellence of this branch of zoology to the law of evolution, since it is obvious that it could not possibly have been deduced from comparison of living animals but only through the long perspective gained by comparison of animals succeeding each other in time.
The climate in late geologic time was very different from that which prevails to-day.
Brown; folios 26, 28, 32, 34, 44, 69, 7 2, 77 and 160 of the Geologic Atlas of the United States; M.