These fossils belong to the genera Solarium or Euomphalus, Pleurotomaria, Natica, Pecten, Trigonia, Terebratula, Spirifer, Orthis, Leptaena, Productus, Turbinolia, Ceriopora, and Retopora. Of twenty-six species collected by M. d'Orbigny, twelve, or nearly the half, have the greatest analogy with the fossils of the carboniferous series of Europe, and of these, three, viz., Spirifer Pentlandi, Spirifer Roissyi, and Productus Villiersi, are quite identical with the same species from Belgium and Russia. We have the same genera; also species having a common facies, and three of them quite identical. The whole facies of the fossils is so analogous, that at first sight we might imagine that we were looking at the usual species met with in the carboniferous rocks of Europe.

Among the fossils which do not belong to the carboniferous series of Europe we must remark a Trigonia (Trigonia antiqua), a genus which has not hitherto been noticed below the Jurassic formations. This curious discovery shews that M. d'Orbigny has understood how to ascertain, not only the resemblances of the American formations to ours, but also the differences between them,-differences which might well be expected at a distance 6000 miles, and which it is only surprising have not been found to be more considerable.

After the Silurian and Devonian periods, the American seas thus supported a different fauna from that of the two first epochs, and one completely analogous in character to that which lived during the carboniferous period in the seas of Europe. This analogy does not now exist between the faunas of the seas of Europe and of South America; and, as M. d'Orbigny remarks, it indicates, in the ancient geological periods, an uniformity of climate no longer observable. These inferences have so much the more weight, from being in this case supported on a triple basis. We have already spoken of the fossils which have induced M. d'Orbigny to refer the system of clay-slates of the Bolivian mountains to the Silurian system of Mr Murchison, and the system of quartzose sandstones to the Devonian system. Here, then, we have in South America, three members of the great palæozoic system, succeeding one another in the same order as the members of the same system in Europe, with which they have respectively the VOL. XXXVI. NO. LXXI.-JAN. 1844.

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greatest analogy, Now, although we may retain some doubts as to the exactitude of the identification of these different formations considered individually, it seems difficult to avoid regarding it as certain that the paleozoic system of South America corresponds as a whole with that of Europe, and that it is subdivided in an analogous manner. This great fact, which has been completely demonstrated by M. d'Orbigny, appears to us to be one of the most important with which geology has been enriched of late years.

Triassic System.-Succeeding the paleozoic formations, and immediately above the carboniferous sandstones of M. d'Orbigny, there is in South America a system of beds which he refers to the Trias of Europe, and which Mr Pentland* likewise considers as its representative. This identification we regard as indicated with plausibility by the observations made, but still not so rigorously established as that of the palæozoic system.

The presumed triassic deposits of Bolivia are composed of an alternation of magnesian limestones, of variegated clays, and of friable argillaceous sandstones. The lowest beds consist of a magnesian compact limestone, which is frequently divided into very thin waved laminæ. M. d'Orbigny has seen this member of the formation, having but a small thickness, near Laguillos, and in the valley of Miraflor. Above these limestones there lie, at the same localities, laminated rosecoloured or variegated clays, which often abound in crystals of gypsum. Above the clays, in the valley of Miraflor, there are compact magnesian limestones, in which M. d'Orbigny discovered numerous fossils, but unfortunately he is unable to particularize more than one species, the others having been lost. This species, the Chemnitzia potonensis, belongs to a new genus of turreted shells, which approaches the Melanias.

The rocks mentioned above are very analogous to those which constitute the trias group in Europe. The limestones of the Muschelkalk, in the north-east of France, and in the department of the Var, as well as the grès bigarrés of the

It is much to be regretted that Mr Pentland has not yet published the valuable results of his extensive scientific investigations in South America.EDIT.

same districts, have recalled to M. d'Orbigny the aspect of the rocks of Bolivia, which he compares with them. The American formations, whose nature and position thus lead us to refer them, at least provisionally, to the Trias, but whose paleontological characters are still almost unknown, seem reduced to occupy, at the present day, and that in the form of large detached portions, the two slopes of the eastern Cordillera of the Bolivian system, and they there attain, at their highest elevation, a height of 4000 yards above the level of the sea. They are probably the remains of a great whole which covered the surface before the occurrence of the geological catastrophes that impressed the present forms on its external physiognomy.

Absence of the Jurassic System.-One of the most remarkable circumstances in American Geology is the absence of the Jurassic formations, a fact announced a long while ago by Von Buch. M. d'Orbigny did not find a single fossil which seems to belong to that period. The only exception to the general rule hitherto brought forward is, that M. d'Orbigny saw some Jurassic Terebratulæ among the fossils collected by M. Domeyko from a limestone in Chili.

Cretaceous Period. The deposits of the cretaceous period seem, on the contrary, to have been very much developed on the American continent, as is proved by the collections of fossils made by Von Humboldt, Boussingault, Degenhardt, and by the geologists of Dumont d'Urville's last voyage, Doctors Hombron and Le Guillou. They occur from Columbia to Tierra del Fuego, or over the whole length of South America, whilst nevertheless they are interrupted in the middle. At that epoch there lived in America as in Europe, particular forms of Ammonite and Ancyloceras, &c.; and independently of the general resemblance of the forms, there were in Columbia and in the Parisian basin enough of identical species to induce us to suppose, that there was a direct communication between the European and the Columbian portions of the Cretaceous sea. It is well known that this sea formed in France two great distinct basins, the Parisian and the Mediterranean. It appears that this same sea covered with its waters not only a considerable portion of Columbia, but generally a large part of the regions situated on the north, the

west, and the south of the continent which then existed in those latitudes. The identity of the fossils of the chalk formation with those of the same formation in Europe, is not so great as regards the south of the American continent as it is in respect to the north, a circumstance which of course indicates a less direct communication. Perhaps we may infer the existence of some long piece of land, which continued as far as America the separation existing in Europe between the Parisian basin and the basin of the Mediterranean.

Tertiary System.-Another geological fact, and it is one of the most remarkable, is the immense extent of the Tertiary system in South America. When we compare it with the small basins disseminated throughout Europe, we are led to believe, along with M. d'Orbigny, that the smallness of the latter is an exception. The tertiary basin of the Pampas terminates and sinks under the Atlantic ocean, from the mouth of La Plata to the Straits of Magellan. Proceeding to the north from this last point, its limits, more or less remote from the Cordilleras, are still uncertain; but every thing leads us to believe, that the deposit of this epoch occupies the plains to the very base of the lateral chains. Advancing still farther to the north, the tertiary basin of the Pampas extends to the foot of the primitive hills of the province of Chiquitos; and it even appears that it is prolonged on all sides without interruption through these hills, into the great basin of the Amazon. Regarding only the portion situated to the south of the primitive hills of Chiquitos, the tertiary basin of the Pampas extends in the direction of the meridian, from the 17th to the 52d degree of south latitude, over a distance of upwards of 2400 miles. Its greatest breadth is about 800 miles.

Throughout this vast extent, and even at the foot of the northern declivity of the hills of Chiquitos, M. d'Orbigny has distinguished, in the American tertiary deposit, three different series, belonging to three successive epochs, viz. 1. The lower beds, destitute of organic remains, which he designates by the name of the Guaranian Tertiary Formation; 2. A middle portion, evidently marine, containing shells belonging to extinct species, and which he calls the Patagonian Tertiary Formation and, 3. An upper portion, containing only skeletons

of mammifera, which he terms the Pampean Loam (Limon Pampéen). The last is only covered by the deposits of the present period.

The Guaranian Tertiary formation is generally composed of three conformable beds. The first consists of ferruginous sandstone, often abounding in nodules of red oxide or hydrate of iron, and in very beautiful agates (sardoines) of various colours, whose angles are much rounded. It has a thickness of upwards of 300 feet, where it is most fully developed. The second bed, termed by M. d'Orbigny Calcaire à fer hydraté, is a greyish-white argillaceous limestone, filled with harder nodules, which are often very compact, with pebbles of quartz, and with rounded grains of hydrate of iron. Its greatest thickness is about 13 feet. The third bed constitutes the upper part of the Guaranian formation, and is composed of grey gypseous clay, filled with hard nodules. It is of the same nature as the preceding bed, but contains no hydrate of iron, that substance being replaced by a large number of nodules of gypsum disseminated in beds through the clay. Its greatest thickness is about 13 feet. M. d'Orbigny found no fossils in any of these three beds. All of them occur with great uniformity in the province of Corientes; and are not absolutely horizontal, but, on the contrary, exhibit undulations and other variations. The upper gypseous clays retain the water, and thus there are produced, at the surface, immense marshes and numerous small lakes, which give rise to one of the most remarkable features of the topography of the country. Beyond the great basin of the Pampas, M. d'Orbigny found the Guaranian Tertiary Formation in the provinces of Chiquitos and Moxos, and even between the 12th and 13th degrees of southern latitude, near San Ramon and San Joaquin, and at the fort of Beira. The points where it is apparent in the province of Moxos seem to form part of a horizontal deposit, an arrangement which leads to the belief that the Guaranian formation levelled the inequalities of the surface before the deposition of the Pampean formation which reposes on it.

The second system of tertiary beds, termed by M. d'Orbigny the Patagonian Tertiary Formation, occupies a much greater extent than the Guaranian tertiary formation. M. d'Orbigny