greatest breadth of the trunk of the larger tree was about one foot, and it diminished from this very gradually for about fifteen feet, which is the extreme length to which they have been uncovered. The stem of the larger tree was divided transversely at nearly regular intervals of about fourteen inches by a cleft or notch, which corresponded to a similar ridge or prominence in the sandstone, both above and below. The two trees are not in the same plane, as may be seen in the sketch which correctly represents the smaller tree in the foreground as about two feet below the larger and three feet distant from it. The cast or impression of the larger tree gives its characters more distinctly than the stem itself: and this impression also measures in diameter considerably more than the trunk which it represents, showing that the latter has shrunk from its original dimensions.

The thickness of deposits over these trees is not more than six feet of sandstone and the same amount of diluvium; but this gives us no idea of the thickness which has undoubtedly been removed by denudation. A microscopical examination of specimens of the trunks of these two trees has been kindly undertaken by my friend, Prof. J. W. Bailey of West Point, who confirms the supposition that they were coniferous. No cones or leaves could be detected in this locality, nor had any such, or in fact any other fossils, been obtained by the quarrymen, although there is a tradition that many years since, trunks of trees were found in a quarry near the present one. Mr. Manross has made particular search here for footmarks similar to those found in other parts of this deposit, but without success. By the zeal and good management of this young gentleman, about four feet in length of the larger tree was successfully removed with its corresponding capping of sandstone, and now forms one of the ornaments of the geological collection of Yale College. The writer supposes that this is the first instance in which the trunks of hard-wooded trees have been observed in situ in the Connecticut sandstone. Fragments of agatized wood have been found in Massachusetts by Prof. Hitchcock, and in the smaller secondary basin of Southbury, Ct., and large stems of reed-like plants are found in the beds which furnish the fish at Middlefield in the same state. B. SILLIMAN, Jr.

Yale College Laboratory, June 1, 1847.

7. Observation on the Basaltic Formation on the northern shore of Lake Superior; by T. R. DUTTON, (communicated for this Journal.)The display of igneous rocks on the north shore of Lake Superior is one of great interest to the geologist, both on account of the variety of the different formations, their relations to the adjacent slates, and the fact that some of them are the repositories of copper and silver.— Among these instructive rocks may be found, granite of a more recent date than the Devonian strata, sienite, porphyry, greenstone and trap, both compact, amygdaloidal and basaltic. It is of the last-mentioned formation that we now speak.

The numerous islands which occupy the most northern part of the lake are composed of trap and porphyry with underlying sandstone, and must be considered as one of the most important parts of the metalliferous region of the northern shore. On the southern shore of Simpson's Island and the southeastern of St. Ignace, the two largest of

these islands, the trap presents the columnar form which is represented in the accompanying cut (drawn by Capt. Stannard) of a section forty feet long and twenty feet high.

The cliffs of this formation which extend for a distance of about three miles, are rarely more than sixty feet in height, and are composed of columns which are usually pentagonal or hexagonal in form, and which, though they are for the most part nearly perpendicular, are often inclined at different angles and sometimes bent. They are twenty or thirty feet long, and from six to eighteen inches in diameter; but they seldom present that distinctness in their columnar structure, and the transverse joints, which characterize the basalt of the Giant's Causeway.

1. Notes on a Tour to Madeira, Teneriffe and Cape Verds, from the Journal of the Voyage of Dr. J. R. T. VOGEL to the Niger, (Lond. Jour. Bot., No. Ixiii, March 1, 1847, p. 125.)-The Island of Madeira contains six hundred and seventy-two species of flowering plants and Ferns, of which eighty-five are absolutely peculiar, and four hundred and eighty common to Europe; two hundred and eighty are common to Madeira and the Azores (whose Flora is estimated at four hundred and twenty-five species); three hundred and twelve (or probably more) to Madeira and the Canaries; and one hundred and seventy to the neighborhood of Gibraltar (where four hundred and fifty-six have been collected).

It is remarkable that out of four hundred European (and these Mediterranean) species, indigenous to Madeira, not more than one hundred and seventy occur in Gibraltar; for it were natural to suppose that the majority of four hundred and eighty species which are very widely dispersed throughout the S. of Europe, should have migrated by way of Gibraltar, if transported across the ocean to Madeira. It is further worthy of observation, that the Azores, though very far to the westward, and the Canaries to the south, both contain many more of the Mediterranean plants seen in Madeira, than does Gibraltar.

A considerable number of the Madeira plants belong to genera not found in the adjacent continent, but in the Canaries, Azores, or Cape de Verd Islands; thus indicating a botanical affinity between these groups, and confined to them.

The evidence of this relationship is very decided, from the peculiarity of the genera or species giving rise to it. Though comparatively few in number, their characters are so prominent and so widely different from the Mediterranean plants which accompany them, that the lat ter, though numerically much the greatest, seem superadded, and, as it were, intruders on the former.

The Canaries and Madeira, from their central position and various other causes, are the centre of this botanical region, called by Mr. Webb the "Macronesian," and exhibit more peculiarity than the Cape de Verds, (as far as they are at present known,) or the Azores. There can be little doubt that Madeira was even more peculiar in its vegetation than now, previous to the destruction by fire of the luxuriant forests, which, according to historic evidence, clothed almost all the lower parts of the island. Not only would such a catastrophe destroy species, but their place would be afterwards occupied by strong-growing imported weeds, which would prevent the reappearance of the native plants by monopolizing the soil.

With very few exceptions, the Mediterranean are the only plants found in Madeira and the Canaries besides what are confined to those islands; in the Azores, on the other hand, some Northern European species are associated with them. In the Cape de Verds, far to the south, W. African and W. Indian plants replace those of the Mediter

ranean.

The Island of Madeira participates in the flora of the W. Indies to a much greater degree than does any part of the adjacent continent :— that this is in a great measure due to the dampness of its insular climate, is clear, from the plants in question being almost entirely Ferns, viz. :-Acrostichum squamosum, Sw. Aspidium molle, Sw. Asplenium monanthemum, Sw. Asplenium furcatum, Sw. Trichomanes radicans, Sw., species found no where on the continent of Europe, nor in N. Africa. The presence of a plant belonging to the otherwise exclusively American genus, Clethra, is striking, because indicating a further relationship with the Flora of the New World, but of a very different character from the above.

The Helichrysa of Madeira are allied in rather a remarkable degree to the S. African species of that genus; a fact which reminds us that the Myrsine Africana, a Cape of Good Hope plant, is a native of the Azores, but of no intervening latitude on the West coast of Africa or the Atlantic Islands, or indeed any where else but Abyssinia. Though not a subject falling immediately within the province of the pure botanist, it may not be amiss here to state, that the four Island-groups in question have been conceived by my friend, Professor Forbes, to be the remains of one continuous and extended tract of land, which formed the western prolongation of the European and African shores. He points to the identity of species between these islands and Europe, as affording botanical evidence of this ingenious theory, which, how

ever, he chiefly rests on geological grounds. Regarded in this light, the question will resolve itself, in the opinion of most botanists, into one, concerning the power of migration, and the probability of migra tion having taken place, to a very great extent, over the Atlantic Ocean, and against the prevailing direction of the winds. It may be contended that such a migration would have peopled these islands solely, or mainly, with certain of the more transportable classes of plants; and that the result must be, that the number of species belonging to each natural order would be great in proportion to the facility with which they bear transportation; while only those orders could be numerous, which possess that faculty in an eminent degree. But such are not the characteristics of the Mediterranean plants found in Madeira.

On the other hand, the existence of such a continent, during the period when these islands bore the plants which they now produce, would argue the former presence of a very large Flora belonging to the type which now distinguishes the islands in question from the Mediterranean, and of whose previous existence the remaining species, peculiar to them, are the indication. Against this theory it might be urged, that more specific identity between the plants of the several insular groups than now is seen, would then be the natural consequence; for the affinity of vegetation between the different islands consists, not in identical species, but in representatives. The same agent, in short, which effected the peopling of the several groups with the plants of conti nental Europe, would also have distributed more equally the nonEuropean species over the same area.

It is, however, to the lofty peaks of Atlas that we must look, if any where, for the continental representatives of those peculiar plants which mark the North Atlantic Insular Floras. Thus, we expect to find the productions of the Galapagos Archipelago on the higher levels of the Cordillera; and the mountains of St. Thomas, Fernando Po and the Cameroons, on the west coast of tropical Africa, may yet exhibit to us the botanical features of St. Helena. Outlying and high islands commonly partake in the peculiar vegetation of a climate cooler than belongs to the low lands of the adjacent continent; though, in the case of Juan Fernandez, they sometimes exhibit genera equally isolated in botanical affinities as their habitats are in geographical position.

Teneriffe.-The next point visited by the Niger Expedition, after leaving Madeira, was the Island of Teneriffe, where the vessel in which Vogel had embarked remained but a few hours. The same island, and the same port, Santa Cruz, had been touched at by the Antarctic Expedition during the previous winter. Teneriffe is always held to be classic ground by the naturalist, as the opening scene of the labors of Humboldt, who there first appreciated in their full extent the laws governing the geographical distribution of plants. His lifelike pictures of the natural phenomena, observed during an ascent of the famous peak, have given an impulse to many succeeding scientific travellers, which has turned their thoughts and steps from closet studies and the pursuit of natural history at home, to seek far distant scenes, in the West, the East and the South.

The Peak itself is seldom descried: one hurried glimpse of its very apex, from upwards of sixty miles distance, was all we obtained: it SECOND SERIES, Vol. IV, No. 10.—July, 1847.

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then appeared like a little short and broad cone high in the clouds, or rather, as an opaque triangular spot on the firmament. It is difficult to imagine this, the culminant point, to be that mighty mass, at whose base the toil-worn traveller pauses; when, having surmounted four-fifths of the mountain, his heart quails at beholding a "Pelion upon Ossa piled" so sternly, so stony and so steep.

Much and deeply did the officers of Captain Ross and Trotter's Expeditions deplore the necessity of hurrying from this spot, so interesting to the sailor, it being the point to which every circumnavigator first steers, and from whence, with chronometers carefully corrected at its well-determined position, he takes his departure. For years, too, this was the prime meridian; distance in longitude at sea being reckoned from Teneriffe as zero, by all the seafaring nations of Europe at one period and by some it is so still. From the days of the earliest circumnavigators, to the present, we sighted the Peak of Teneriffe" marks that page in the narrative, at which all that is interesting in the voyage commences.

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In the history of geology, the Canary Islands hold a conspicuous position von Buch developed his theory of craters of elevation from what he there observed his name too recalls, and most appropriately, that of his fellow-laborer in the same shores, Christian Smith, the amiable and gifted Swede, who first after Humboldt, explored their botany. Christian Smith returned to Europe to embark in the ill-fated Congo Expedition when he again saw the Peak of Teneriffe, he welcomed it as a familiar object, and bade it adieu, rejoicing that a still more novel field of inquiry was opened to him, beyond this scene of his early exertions. A few short months terminated his life and hopes: like Vogel, he fell a victim to the dreaded fever of the pestilential coast of Africa: like him, too, he was a martyr in the cause of botanical science.

Possessed of so many and such touching associations, no naturalistvoyager can see the Fortunate Isles rising, one by one, on the horizon of the mighty Atlantic, without some feeling of melancholy, while reflecting on the fate of these his two predecessors, both most accomplished naturalists of their age and day; and whose prospects and hopes were in every respect as bright, perhaps brighter, than his own. The excellent and beautiful work of Mr. Webb, on the Natural History of the Canaries, leaves little to be said, especially of their botany; and renders even an enumeration of the few species gathered by Vogel and the Botanist of the Antarctic Expedition unnecessary; for they were all collected within a few miles of Santa Cruz, during a very hurried walk, and scarcely include a dozen kinds. This locality is one of the most barren of the whole group, especially in the immediate neighborhood of the sea. The broad frontage of cliff and mountain, reaching upwards for several thousand feet above the town, and fore-shortened to the view from seaward, presents a progressive increase of verdure from the water's edge to the mountains. At this season, when the vines are out of leaf, nothing green meets the eye; the trees, either isolated or in very small clumps, only dot the alternate ridges and steep gullies with which the slopes are everywhere cut like the edge of a saw, producing that spotty effect in the landscape so admirably transferred to the phytographical illustrations of the work allu