[91] Trans. Swedish Academy, 1871, Journal London Geological Society, vol. xxvlii.
Between 1870 and 1873 my attention was turned to the two sub-floras intermediate between those of the Devonian and the coal formation, the floras of the Lower Carboniferous (Sub-carboniferous of some American geologists) and the Millstone Grit, and in a report upon these[92] similar deductions were expressed. It was stated that in Newfoundland and Northern Cape Breton the coal formation species come in at an early part of that period, and as we proceed southward they belong to progressively newer portions of the Carboniferous system. The same fact is observed in the coal beds of Scotland, as compared with those of England, and it indicates that the coal formation flora, like that of the Devonian, spread itself from the north, and this accords with the somewhat extensive occurrence of Lower Carboniferous rocks and fossils in the Parry Islands and elsewhere in the Arctic regions.[93]
[92] "Fossil Plants of Lower Carboniferous and Millstone Grit Formations of Canada," pp. 47, 10 plates. Montreal, 1873.
[93] G. M. Dawson, "Report on Arctic Regions of Canada."
Passing over the comparatively poor flora of the earlier Mesozoic, consisting largely of cycads, pines, and ferns, which, as we have seen, is probably of southern origin, and is as yet little known in the arctic, though represented, according to Heer, by the supposed Jurassic flora of Cape Boheman, we find, especially at Komé and Atané in Greenland, an interesting occurrence of those earliest precursors of the truly modern forms of plants which appear in the Cretaceous, the period of the English chalk, and of the New Jersey greensands. There are two plant groups of this age in Greenland, one, that of Komé consists almost entirely of ferns, cycads, and pines, and is of decidedly Mesozoic aspect. This was regarded by Heer as Lower Cretaceous. The other, that of Atané, holds remains of many modern temperate genera, as Populus, Myrica, Ficus, Sassafras, and Magnolia. This he regards as Middle Cretaceous. Above this is the Patoot series, with many exogenous trees of modern genera, and representing the Upper Cretaceous. Resting upon these Upper Cretaceous beds, without the intervention of any other formation,[94] are beds rich in plants of much more modern appearance, and referred by Heer to the Miocene period, a reference which appeared at the time to be warranted by comparison with the Tertiary plants of Europe, but, as we shall see, not with those of America. Still farther north this so-called Miocene assemblage of plants appears in Spitzbergen and Grinnell Land; but there, owing to the predominance of trees allied to the spruces, it has a decidedly more boreal character than in Greenland, as might be anticipated from its nearer approach to the pole.[95]
[94] Nordenskiöld, Expedition to Greenland, Geological Magazine, 1872.
[95] Yet even here the Bald Cypress (Taxodium distichum), or a tree nearly allied to it, is found, though this species is now limited to the Southern States. Fielden and De Ranee, Journal of Geological Society, 1878.
If now we turn to the Cretaceous and Tertiary floras of Western America, as described by Lesquereux, Newberry, and Ward, we find in the lowest Cretaceous rocks known there until very recently—those of the Dakota group, which may be in the lower part of the Middle Cretaceous—a series of plants[96] essentially similar to those of the Middle Cretaceous of Greenland. To these I have been able to add, through the researches of Mr. Richardson and Dr. G. M. Dawson, a still earlier flora, that of the Kootanie and Queen Charlotte Island formations, as old as the Gault and Wealden. It wants the broad-leaved plants of the Dakota, and consists mainly of pines, cycads, and ferns; and only in its upper part contains a few forerunners of the exogens.[97] These plants occur in beds indicating shallow sea conditions as prevalent in the interior of America, causing, no doubt, a warm climate in the north. Overlying this plant-bearing formation we have an oceanic limestone (the Niobrara), corresponding in many respects to the European chalk, and containing similar microscopic organisms. This extends far north into the British territory,[98] indicating farther subsidence and the prevalence of a vast Mediterranean Sea, filled with warm water from the equatorial currents, and not invaded by cold waters from the north. This is succeeded by Upper Cretaceous deposits of clay and sandstone, with marine remains, though very sparsely distributed; and these show that further subsidence or denudation in the north had opened a way for the arctic currents, producing a fall of temperature at the close of the Cretaceous, and partially filling up the Mediterranean of that period.
[96] Lesquereux, Report on Cretaceous Flora. The reader not interested in American details may pass over to the middle of page 213.
[97] This flora has since been described in Virginia and Maryland by Fontaine, and has been recognised in Montana by Newberry.