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and their allies, not to mention a corresponding number of carnivorous animals. These herbivora probably fed in a good degree upon herbage and grasses of still existing species. For herbs and grasses are generally capable of enduring much greater climatic changes, and are therefore likely to be even more ancient than trees. These animals must have had at least a warm-temperate climate to live in: so that in lat. 40°-43° they could not have been anywhere near the northern limit of the temperate flora of those days; indeed the temperate flora, which now in Western Europe touches the Arctic Circle, must then have reached equally high latitude in Central, or Western North America. In other words, the temperate floras of America and Asia must then have been conterminous (with small oceanic separation), and therefore have commingled, as conterminous floras of similar climate everywhere do.

At length, as the post-tertiary opened, the glacier epoch came slowly on, an extraordinary refrigeration of the northern hemisphere, in the course of ages carrying glacial ice and arctic climate down nearly to the latitude of the Ohio. The change was evidently so gradual that it did not destroy the temperate flora, at least not those enumerated above as existing species. These and their fellows, or such as survive, must have been pushed on to lower latitudes as the cold advanced, just as they now would be if the temperature were to be again lowered; and between them and the ice there was doubtless a band of subarctic and arctic vegetation,-portions of which, retreating up the mountains as the climate ameliorated and the ice receded, still scantily survive upon our highest Alleghanies, and more abundantly upon the colder summits of the mountains of New York and New England;-demonstrating the existence of the present arctic-alpine vegetation during the glacial era; and that the change of climate at its close was so gradual that it was not destructive to vegetable species.

As the temperature rose, and the ice gradually retreated, the surviving temperate flora must have returned northward pari passu, and-which is an important point-must have advanced' much farther northward, and especially northwestward, than it now does; so far, indeed, that the temperate floras of North America and of Eastern Asia, after having been for long ages most widely separated, must have become a second time conterminous. Whatever doubts may be entertained respecting the existence of our present vegetation generally before the glacial era, its existence immediately after that period will hardly be questioned. Here, therefore, may be adduced the direct evidence recently brought to light by Mr. Lesquereux, who has identified our live oak (Quercus virens), Pecan (Carya oliva formis), Chinquapin (Castanea pumila), Planer-tree (Planera Gme

lina), Honey-Locust (Gleditschia triacanthos), Prinos coriaceus, and Acorus Calamus,-besides an elm and a Ceanothus doubtfully referable to existing species,-on the Mississippi, near Columbus, Kentucky, in beds which Mr. Lesquereux regards as anterior to the drift. Professor D. D. Owen has indicated their position "as about 120 feet lower than the ferrugineous sand in which the bones of the Megalonyx Jeffersonii were found." So that they belong to the period immediately succeeding the drift, if not to that immediately preceeding it. All the vegetable remains of this deposit, which have been obtained in a determinable condition, have been referred, either positively or probably, to existing species of the United States flora, most of them now inhabiting the region a few degrees farther south.

If, then, our present temperate flora existed at the close of the glacial epoch, the evidence that it soon attained a high northern range is ready to our hand. For then followed the second epoch of the post-tertiary, called the fluvial by Dana, when the region of St. Lawrence and Lake Champlain was submerged, and the sea there stood five hundred feet above its present level; when the higher temperate latitudes of North America, and probably the arctic generally, were less elevated than now, and the rivers vastly larger, as shown by the immense upper alluvial plains, from fifty to three hundred feet above their present beds; and when the diminished breadth and lessened height of northern land must have given a much milder climate than the present.

Whatever the cause, the milder climate of the fluvial epoch is undoubted. Its character, and therefore that of the vegetation, is decisively shown, as geologists have remarked, by the quadrupeds. While the Megatherium, Mylodon, Dicotyles, &c. demonstrate a warmer climate than the present in the Southern and Middle United States, the Elephas primigenius, ranging from Canada to the very shores of the Arctic Ocean, equally proves a temperate climate and a temperate flora in these northern regions. This is still more apparent in the species of the other continent, where, in Siberia, not only the Elephas primigenius, but also a Rhinoceros, roamed northward to the arctic sea-coast. The quadrupeds that inhabited Europe in the same epoch are well known to indicate a warm-temperate climate as far north as Britain, in the middle, if not the later post-tertiary. North America then had its herds of Mastodons, Elephants, Buffaloes or Bisons of different species, Elks, Horses, Megalonyx, the Lion, &c.; and, from the relations between this fauna and that of Europe, there is little doubt that the climate was as much milder than the present on this as on the other side of the ocean. All the facts known to us in the tertiary and post-tertiary, even to the limiting line of the drift, conspire to show that the difference between the two continents as to temperature was very nearly the same then

as now, and that the isothermal lines of the northern hemisphere curved in the directions they now do.

A climate such as these facts demonstrate for the fluvial epoch would again commingle the temperate floras of the two continents at Behring's Straits, and earlier-propably through more land than now-by way of the Aleutian and Kurile Islands. I cannot imagine a state of circumstances under which the Siberian Elephant could migrate, and temperate plants could not.

The fluvial was succeeded by the "terrace epoch," as Dana names it, "a time of transition towards the present condition, bringing the northern part of the continent up to its present level, and down to its present cool temperature,"*-giving the arctic flora its present range, and again separating the temperate floras of the New and of the Old World to the extent they are now separated.

Under the light which these geological considerations throw upon the question, I cannot resist the conclusion, that the extant vegetable kingdom has a long and eventful history, and that the explanation of apparent anomalies in the geological distribution of species may be found in the various and prolonged climatic or other physical vicissitudes to which they have been subject in earlier times;-that the occurrence of certain species, formerly supposed to be peculiar to North America, in a remote or antipodal region affords of itself no presumption that they were originated there;-and that the interchange of plants between Eastern North America and Eastern Asia is explicable upon the most natural and generally received hypothesis, (or at least offers no greater difficulty than does the Arctic flora, the general homogeneousness of which round the world has always been thought compatible with local origin of the species,) and is perhaps not more extensive than might be expected under the circumstances. That the interchange has mainly taken place in high northern latitudes, and that the isothermal lines have in earlier times turned northward on our eastern, and southward on our northwest coast, as they now do, are points which go far towards explaining why Eastern North America, rather than Oregon and California, has been mainly concerned in it, and why the temperate interchange, even with Europe, has principally taken place through Asia.

Brasenia peltata.-To the remarks upon the known range of of this species, I have now to add the interesting fact, that it exists upon the northwestern coast of America, having been gathered by Dr. Pickering, in Wilkes's South Sea Exploring Expedition, in a stream which falls into Gray's Harbor, lat. 47°. It must be

*For the collocation and communication of the geological data here presented, I am indebted to the kindness of my friend, Professor Dana.

local on the western side of the continent, or it would have been met with before. When this remarkable plant was known to occur only in Eastern North America and Eastern Australia, it made the strongest case in favor of double creation that perhaps has ever been adduced. But since it has been found to occur throughout the Eastern Himalayas and in Japan, and has now been detected in Northwestern America also, the case seems to crown the conclusions to which this memoir arrives.

ART. XXI.-Supplement to an Enumeration of North American Lichens, continued; by EDWARD TUCKERMAN, A.M., Professor of Botany in Amherst College.

THE species follow each other, as before, in the order of the arrangement proposed by Dr. Nylander, who has studied these plants in the light afforded by a knowledge which includes not only the external, but all the microscopical details. Some species, not North American as yet known, but of more or less interest in connection with our flora, are added in brackets.

COLLEMA APALACHENSE, Tuck. in litt., thallo stellato multifido imbricato crassiusculo fusco-viridi, laciniis plano-convexis apice subteretibus obtusis rugulosis, subtus pallidis; apotheciis innatosessilibus planis rufescentibus margine integerrimo. Sporæ ellipsoidea 3-septatæ diam. vix duplo longiores. Lime-rocks, Hancock county, Alabama, Hon. T. M. Peters.

COLLEMA TEXANUM, sp. nova, thallo orbiculari substellato imbricato crasso luteo-virescente, laciniis radiantibus elongatis subplanis profunde pinnato-laceris papulosis; apotheciis sparsis planiusculis rufis margine tumido integro. Sporæ minimæ fusiformes uniseptatæ.-Trees, Texas, Mr. Charles Wright. Resembles the more perfect forms of C. pulposum. Spores exceedingly small. I am indebted, for their detection and delineation, to my friend, the Rev. J. L. Russell.

LEPTOGIUM CRENATELLUM, sp. nova, thallo imbricato tenerrimo glauco-cinerascente, laciniis rotundatis crenatis denticulatis; apotheciis minusculis creberrimis sessilibus convexis pallido-fuscescentibus margine tenui pallescente subintegro evanescente. Sporæ ellipsoidea 5-septatæ.-On trees in swamps, Brattleborough, Vermont, Mr. C. C. Frost.

LEPTOGIUM JUNIPERINUM, Tuck. in litt., thallo pusillo suborbiculari imbricato tenui plumbeo e lobis rotundatis adscendentibus crenatis subtus ad margines albo-fibrillosis; apotheciis sesilibus plano-convexis margine tenui demum evanido discum rufofuscum cingente. Spora ellipsoideæ apicibus acuta 3-septatæ. -On the earth in cedar woods, Texas. Mr. Wright.

CALICIUM CURTISII, sp. nova, thallo byssaceo nigro (vel obsoleto) apotheciis minutis turbinatis disco subnitido nigro stipitibus brevibus ex albido rufescentibus demum nigris. Spora majusculæ ellipsoideæ vel elongato-ellipsoidea (dactyline, Koerb.) fuscescentes simplices.-On the living bark of Rhus typhina, in Berkshire, Massachusetts; and of Robinia Pseudacacia, at the Hot Springs, Virginia, Rev. Dr. Curtis. The stipes like those of Calicium or Coniocybe nigricans, Fr. (not of Tuckerm. Synops. Lich. N. E. which is C. subtile, on Bark) but the apothecia quite different, and the spores very much larger than in that species; as in C. eusporum, Nyl., to which, and C. byssaceum, Fr., the lichen is probably nearest.

BEOMYCES ABSOLUTUS, sp. nova, thallo crustaceo effuso tenuissimo submembranaceo læteviridi; apotheciis stipitatis incarnatis planis disco demum convexiusculo marginem tenuem excludente. Sporæ ellipsoideæ simplices hyalinæ. Biatora icmadophila, var. stipitata, Tuckerm. in litt. ad cel. Montagne.-On the earth, Alabama, Mr. Peters. [Mountains of Cuba, Mr. Wright. Venezuela, Mr. Fendler.] Representing possibly, in tropical America, both B. ericetorum (B. roseus, Auctt.) and B. æruginosus (Biat. icmadophila, Auctt.) but nearest to the last, which it seems to connect, naturally, with the first.

[CLADONIA DACTYLOTA, sp. nova, thalli squamulis amplis erectis subtus albo-pulverulentis podetia gracilescentia cylindrica membranaceo-corticata lævigata viridi-pallescentia e margine proferentibus, scyphis angustatis margine subincurvis denticulatis demum oblique prolifero-palmatis; apotheciis carneo-fuscescentibus.

Var. B, symphycarpia, podetiis elongatis scyphis subintegris (vel obsoletis) apotheciis conglomeratis.

Var. 7, sorediata, podetiis hinc inde, scyphisque, vel his obliteratis apicibus clavatis cornutisve sorediis pulvinatis albis adspersis. On the earth in the mountains of Cuba, Mr. Wright. Venezuela, Mr. Fendler. Differs from C. fimbriata as C. digitata differs from C. deformis. The primary form is hardly distinguishable from C. digitata, except in being whiter, and in the color of the apothecia. The white, cushion-like, powdery soredia, which, in what seems to be the commonest state, take the place of the apothecia, and are scattered over the smooth podetia (in the latter case appearing clearly to be deliquescent squamules) make perhaps the most striking, however an abnormal feature of this elegant Cladonia.]

STEREOCAULON NANODES, sp. nova, podetiis pumilis erectis cæspitoso-conglomeratis subnudis validis tereti-compressis a basi vage apicemque versus fastigiato-ramosis albidis, phyllocladiis ad apices confertis e rotundato-subsquamaceis glaucis demum

SECOND SERIES, VOL. XXVIII, No. 83.-SEPT., 1859.

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