The names Tertiary and Quaternary are remnants of an old geological nomenclature which has lost its significance, and were proposed when the whole succession of strata was believed to be divisible into four groups, called the Primary, Secondary, Tertiary, and Quaternary, respectively. When it was learned that there were groups and systems much older than the so-called Primary, the name Palaeozoic was substituted for Primary, as was Mesozoic for Secondary, though the latter term is still used, especially in England. The name Tertiary has thus lost its meaning, but is nevertheless retained as a division of the Cenozoic group or era.

Tertiary Formations Of The United States

The great revolution which closed the Cretaceous and inaugurated the Tertiary has left its effects visible in all the continents, but the gap between the two periods is not everywhere the same. This revolution gave to North America nearly its present outlines, except for the land connections with Europe and Asia, which were from time to time interrupted and renewed. In consequence of this, marine Tertiary beds occur only along the borders of the continent, while the Tertiary of the interior is all of continental origin. In other continents, and especially in Europe, the distribution of land and sea was very different in the Tertiary from what it is now, and the topography of the land was profoundly altered in the course of the period. Some of the highest mountain ranges of the earth were upheaved in Tertiary times, such as the Atlas, the Alps, the Caucasus, and the Himalayas, and many ranges of earlier date were subjected to renewed compression and upheaval. That Tertiary mountains are high-is not due to any extreme degree of compression as compared with that which produced older ranges, but merely to the youth of the former; denudation has not yet had time to sweep them away.

Fig. 303. - Map of North America in the Tertiary period. Black areas = known exposures of marine Tertiary; white = land; lined areas = sea; dotted areas = continental formations .

The Tertiary system or period is divisible into five well-distinguished series or epochs, which may usually be identified in both the marine and continental formations; but for lack of common fossils .it is not yet possible to correlate the stages and substages of the interior region with those of the coast. In the preceding table, therefore, no exact comparison of these minor subdivisions is intended.

The name Tertiary was given by Cuvier and Brongniart, early in the last century, to the succession of marine, brackish-water, and fresh-water beds in the Paris basin. Sir Charles Lyell many years later proposed the division of the Tertiary into three parts, Eocene (from the Greek eos, the dawn, and kainos, recent), Miocene {melon, less, and kainos), and Pliocene (pleion, more, and kainos), a scheme which is still used, modified by Beyrich through the insertion of a fourth epoch, the Oligocene {oligos, little or in small degree, and kainos). Last of all, the lower Eocene has been separated under the name Paleocene (palaios, ancient, as in Palaeozoic) a change proposed thirty years ago by the botanist Schimper, but only lately coming into wider favour. It has become customary to distinguish between the older and newer parts of the Tertiary by grouping together the Eocene and Oligocene into the Palceogene, and the Miocene and Pliocene into the Neogene. Eocene and Neocene are employed in the same way, but this is objectionable because it is using Eocene in two different senses.