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refuge to plants in times of submergence, and means of escape to the south in times of refrigeration. Hence, the greater continuity of American vegetation and the survival of genera like Sequoia and Liriodendron, which have perished in the Old World. Still, there are some exceptions to this, for the gingko-tree is a case of survival in Asia of a type once plentiful in America, but now extinct there. Eastern Asia has had, however, some considerable share of the same advantage possessed by America, with the addition, referred to by Gray, of a better and more insular climate.

But our survey of these physical conditions can not be considered complete till we shall have considered the great Glacial age of the Pleistocene. It is certain that throughout the later Miocene and Pliocene the area of land in the northern hemisphere was increasing, and the large and varied continents were tenanted by the noblest vegetation and the grandest forms of mammalian life that the earth has ever witnessed. As the Pliocene drew to a close, a gradual diminution of warmth came on, and more especially a less equable climate, and this was accompanied with a subsidence of the land in the temperate regions and with changes of the warm ocean-currents. Thus gradually the summers became cooler and the winters longer and more severe, the hill-tops became covered with permanent snows, glaciers ploughed their way downward into the plains, and masses and fields of floating ice cooled the seas. In these circumstances the richer and more delicate forms of vegetation must have been chilled to death or obliged to remove farther south, and in many extensive regions, hemmed in by the advance of the sea on the one hand and land-ice on the other, they must have altogether perished.

Yet even in this time vegetation was not altogether extinct. Along the Gulf of Mexico in America, and in the Mediterranean basin in Europe, there were still some remains of a moderate climate and certain boreal and arctic forms moving southward continued to exist here and there in somewhat high latitudes, just as similar plants now thrive in Grinnell Land within sight of the snows of the Greenland mountains. A remarkable summary of some of these facts as they relate to England was given by an eminent English botanist, Mr. Carruthers, in his address as President of the Biological Section of the British Association at Birmingham in 1886. At Cromer, on the coast of Norfolk, the celebrated forest-bed of newer Pliocene age, and containing the remains of a copious mammalian fauna, holds also remains of plants in a state admitting of determination. These have been collected by Mr. Reid, of the Geological Survey, and were reported on by Carruthers, who states that they represent a somewhat colder temperature than that of the present day. I quote the following details from the address.

With reference to the plants of the forest-bed or newer Pliocene he remarks as follows:

“Only one species (Trapa natans, Willd.) has disappeared from our islands. Its fruits, which Mr. Reid found abundantly in one locality, agree with those of the plants found until recently in the lakes of Sweden. Four species (Prunus speciosa, L., Enanthe Tichenalii, Sm., Potamogeton pterophyllus, Sch., and Pinus abies, L.) are found at present only in Europe, and a fifth (Potamogeton trichoides, Cham.) extends also to North America; two species (Peucedanum palustre, Moench, and Pinus sylvestris, L.) are found also in Siberia, while six more (Sanguisorba officinalis, L., Rubus fruticosus, L., Cornus sanguinea, L., Euphorbia amygdaloides, L., Quercus robur, L., and Potamogeton crispus, L.) extend into western Asia, and two (Fagus sylvatica, L., and Alnus glutinosa, L.) are included in the Japanese flora. Seven species, while found with the others, enter also into the Mediterranean flora, extending to North Africa : these are Thalictrum minus, L., Thalictrum flavum, L., Ranunculus repens, L., Stellaria aquatica, Scop., Corylus avellana, L., Yannichellia palustris, L., and Cladium mariscus, Br. With a similar distribution in the Old World, eight species (Bidens tripartita, L., Myosotis cæspitosa, Schultz, Suæda maritima, Dum., Ceratophyllum demersum, L., Sparganium ramosum, Huds., Potamogeton pectinatus, L., Carex paludosa, Good., and Osmunda regalis, L.) are found also in North America. Of the remainder, ten species (Nuphar luteum, Sm., Menyanthes trifoliata, L., Stachys palustris, L., Rumex maritimus, L., Rumex acetosella, L., Betula alba, L., Scirpus pauciflorus, Lightf., Taxus baccata, L., and Isoetes lacustris, L.) extend round the north temperate zone, while three (Lycopus europæus, L., Alisma plantago, L., and Phragmites communis, Trin.), having the same distribution in the north, are found also in Australia, and one (Hippuris vulgaris, L.) in the south of South America. The list is completed by Ranunculus aquatilis, L., distributed over all the temperate regions of the globe, and Scirpus lacustris, L., which is found in many tropical regions as well.”

He remarks that these plants, while including species now very widely scattered, present no appreciable change of characters.

Above this bed are glacial clays, which hold other species indicating an extremely cold climate. They are few in number, only Salix polaris, a thoroughly arctic species, and its ally, S. cinerea, L., and a moss, Hypnum turgescens, Schimp., no longer found in Britain, but an Alpine and arctic species. This bed belongs to the beginning of the Glacial period, the deposits of which have as yet afforded no plants in England. But plants occur in post-glacial and upper-glacial beds in different parts of England, to which Carruthers thus refers : “The period of great cold, during which arctic ice


extended far into temperate regions, was not favorable to vegetable life. But in some localities we have stratified clays with plant-remains later than the Glacial epoch, yet indicating that the great cold had not then entirely disappeared. In the lacustrine beds at Holderness is found a small birch (Betula nana, L.), now limited in Great Britain to some of the mountains of Scotland, but found in the arctic regions of the Old and New World and on Alpine districts in Europe, and with it Prunus padus, L., Quercus robur, L., Corylus avellana, L., Alnus glutinosa, L., and Pinus sylvestris, L. In the white clay-beds at Bovey Tracey of the same age there occur the leaves of Arctostaphylos uva-ursi, L., three species of willow, viz., Salix cinerea, L., S. myrtilloides, L., and S. polaris, Wahl., and in addition to our Alpine Betula nana, L., the more familiar B. alba, L. Two of these plants have been lost to our flora from the change of climate that has taken place, viz., Salix myrtilloides, L., and S. polaris, Wahl.; and Betula nana, L., has retreated to the mountains of Scotland. Three others (Dryas octopetala, L., Arctostaphylos uva-ursi, L., and Salix herbacea, L.) have withdrawn to the mountains of northern England, Wales, and Scotland, while the remainder are still found scattered over the country. Notwithstanding the diverse physical conditions to which these plants have been subjected, the remains preserved in these beds present no characters by which they can be distinguished from the living representatives of the species.”

One of the instances referred to is very striking. At Bovey Tracey the arctic beds rest directly on those holding the rich, warm temperate flora of the Eocene; so that here we have the evidence of fossil plants to show the change from the climate of the Eocene to that of arctic lands, and the modern vegetation to indicate the return of a warm temperature.

In Canada, in the Pleistocene beds known as the Leda clays, intervening between the lower boulder clay and the Saxicava sand, which also holds boulders, there are beds holding fossil plants, in some places intermixed with sea-shells and bones of marine fishes, showing that they were drifted into the sea at a time of submergence. These remains are boreal rather than arctic in character, and with the remains of drift-wood often found in the boulder deposits serve to indicate that there were at all times oases of hardy life in the glacial deserts, just as we find these in polar lands at the present day. I condense from a paper on these plants * the following facts, with a few additional notes :

The importance of all information bearing on the temperature of the Post - pliocene period invests with much interest the study of the land-plants preserved in deposits of this age. Unfortunately, these are few in number, and often not well preserved. In Canada, though fragments of the woody parts of plants occasionally occur in the marine clays and sands, there is only one locality which has afforded any considerable quantity of remains of their more perishable parts. This is the well-known deposit of Leda clay at Green's Creek, on the Ottawa, celebrated for the perfection in which the skeletons of the capelin and other fishes are preserved in the calcareous nodules imbedded in the clay. In similar nodules, contained apparently in a layer somewhat lower than that holding the ichthyolites, remains of land-plants are somewhat abundant, and, from their association with shells of Leda glacialis, seem to have been washed down from the land into deep water. The circumstances would seem to have been not dissimilar from those at present existing in the northeast arm of Gaspé Basin, where I have dredged from mud now being deposited in deep water, living

*“Canadian Naturalist,” 1866.

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