referred. The English geognosts look upon the continent for their lias and red marl; the German for their bunte sandstein and muschelkalk. These words present themselves in the minds of travellers associated with remembrances of localities. It is not of so much importance, therefore, to produce precise ideas, as to make choice of localities generally known, and which are celebrated, either by the working of mines, or by descriptive works.

In order to diminish the effects of national vanity, and to attach new names to more important objects, I proposed a long time ago, (1795), the denomination of Alpine Limestone, and Jura Limestone. A portion of the High Alps of Switzerland, and the greater part of Jura, are without doubt formed of these two rocks: the names, however, generally received at the present day, of Alpine Limestone (Zechstein), and Jura Limestone, should in my opinion be modified or entirely abandoned. The lower beds of the Jura mountains, filled with gryphites, belong to an older formation, perhaps to the zechstein; and a great part of the limestone of the Alps of Switzerland assuredly is not zechstein; but, according to Messrs de Buch and Escher, transition limestone. It would therefore be better to choose the geographical names of rocks from among the names of isolated mountains, the whole visible mass of which belongs only to a single formation, than to derive them, as I have erroneously done, from entire chains. I have thought, and many geognosts have formed the same opinion, that the Jura limestone (cavernous limestone of Franconia) was generally placed upon the continent, beneath the Nebra sandstone, (bunte sandstein), between this sandstone and the zechstein. Subsequent observations have proved, that the name of Jura Limestone had with reason been applied to rocks which are very distant from the mountains of Western Switzerland; but that the true geognostical place of this formation, (when there is not a suppression of the inferior formations), occurs above the Nebra sandstone, between the shelllimestone (muschelkalk, or the quadersandstein), and the chalk. A geographical name, justly applied to several analogous rocks, renders us attentive to their identity of relative position; but the place which homonymous rocks ought to occupy in the total series, is not well determined except when the geographical name has been selected, after having acquired a perfect certainty regarding their position. Circumstances are the same with regard to the relative age of the molasse of Argovia, (nagelfluhe and of the Pirna quadersandstein (grès blanc of M. de Bonnard), two rocks of very recent

origin, which have been very well examined separately, but whose relations to each other, and to the chalk and Jura limestone, have only been illustrated of late. One may therefore be pretty sure of having met in the New Continent with rocks identical with the molasse or quadersandstein, without being able to pronounce with certainty upon their relations with all the secondary or tertiary rocks. When rocks are not immediately in contact, and are not covered by deposites of known position, their relative age can only be conjectured from simple analogies.

The terms of the geognostical series are either simple or complex. To the simple terms belong the greater number of the primitive formations: the granites, gneisses, mica-slates, clay-slates, &c. The complex terms occur in greater num bers among the transition rocks: there, each formation includes an entire group of rocks, which alternate periodically. The terms of the series are not transition limestones or greywackes, constituting independent formations; they are associations of clay-slate, green-stone, and greywacke; of porphyry and greywacke; of granular and steatitic limestone, and of conglomerates, composed of primitive rocks; of clay-slate and black limestone. When these associations are formed of three or four rocks which alternate, it is difficult to give them significant names,→→ names indicative of the whole composition of the group,-of all the partial members of the complex term of the series. It may then assist in fixing the groups in the memory, to retrace the rocks which predominate in them, without being absolutely wanting in the neighbouring groups. It is in this manner that the granular steatitic limestone characterises the Tarantaise formation; the greywacke, the great transition formation of the Hartz and of the banks of the Rhine; the metalliferous porphyries rich in hornblende, and almost destitute of quartz, the forma tion of Mexico and of Hungary. If these phenomena of alternation attain their maximum in the transition districts, still they are not entirely excluded from the primitive and secondary terrain. In both of these terrains, complex terms are mixed with the simple terms of the geognostical series. I shall mention among the secondary formations, the sandstone placed below the alpine limestone, (the Nebra sandstone, bunte sandstein), which is an association of marly clay, sandstone and oolites; the limestone which covers the red-sandstone of the coal-formation (the zechstein or alpen-kalkstein), which is a less constant association of limestone, of (muriatiferous) gypsum, of stinkstone and of pulverulent bituminous marl. In the primitive class we find the three first terms of the series; the

oldest rocks either isolated, or alternating two and two, according as they are geognostically more approximated by their relative age, or the whole three alternating. The granite sometimes forms constant associations with the gneiss, and the gneiss with the mica-slate. These alternations follow particular laws: we see, (for example in Brazil, and, although less distinctly, in the maritime chain in Venezuela), the granite, gneiss, and mica-schist in a triple association; but I have not found granite alternating alone with mica-slate, or gneiss and mica-slate alternating by themselves with clay-slate.

We must not confound, and on this point I have often insisted in the present article, rocks passing insensibly to those which are in immediate contact with them; for example, micaslates, which oscillate between gneiss and clay-slate, with rocks which alternate with one another, and which preserve all their distinctive characters of composition and of structure. M. D'Aubuisson has long ago shewn how chemical analysis approximates the clay-slate to mica. (Journal de Physique, vol. lxviii. p. 128; Traité de Geognosie, vol. ii. p. 97). The first, it is true, has not the metallic lustre of mica-slate; it contains a little less potash, and more carbon; the silex does not unite into nodules or thin laminæ of quartz, as in the micaslate; but it cannot be doubted, that scales of mica form the principal base of the clay-slate. These scales are so joined together, that the eye cannot distinguish them in the mass. It is perhaps this same affinity which prevents the alternation of clay-slates and mica-slates: for in these alternations Nature seems to favor the association of heterogeneous rocks; or, to make use of a figurative expression, she delights in the associations whose alternating rocks present a great contrast of crystallization, of mixture, and of colour. At Mexico, I have seen dark greenstones, alternate thousands of times with reddish-white syenites, abounding more in quartz than in felspar. In this greenstone there were veins of syenite, and in the syenite veins of greenstone; but none of the two rocks passed into the other. (Essai politique sur la Nouvelle Espagne, v. ii. p. 523). They present at the limit of their mutual contact, differences as marked as the porphyries which alternate with the greywackes or with the syenites, as the black limestones which alternate with the transition clay-slates, and so many other rocks of entirely heterogeneous composition and aspect. Further, when, in primitive deposites, rocks more related by the nature of their composition than by their struc ture or mode of aggregation, for example, the granites and gneisses, or the gneisses and mica-schists, alternate; these

rocks do not by any means show the same tendency to pass into each other, as they present, when isolated in formations. which are not of a complex character. We have already observed, that often a bed 8, becoming more frequent in the rock, announces to the traveller that the simple formation «, is to be succeeded by a compound formation, in which a and ẞ alternate. Farther on, it happens, that assumes a greater development; that is no longer an alternating rock, but a simple bed subordinate to s, and that this rock & shows itself alone, until, by the frequent repetition of beds 7, it becomes the precursor of a compound formation ß, alternating with 7. We might substitute for these signs the words granite, gneiss, and mica-slate; those of porphyry, greywacke, and syenite; of gypsum, marl, and fetid limestone (stinkstein). Pasigraphic language has the advantage of generalizing the problems; it is more conformable to the wants of geognostical philosophy, of which I attempt to present here the first elements, in so far as they have relation to the study of the superposition of rocks. Now, if often between formations which are simple and very closely allied, in the order of their relative antiquity, between the formations, 6, 7, there occur compound formations interposed, and 6, (that is to say, a alternating with ß, and ß alternating with 2); we observe, also, although less frequently, that a formation (for example ), assumes so extraordinary an increase, that it envelopes the formation ; and that 8, instead of showing itself as an independent rock, placed between « and % is now nothing but a bed in a. It is thus, that, in Lower Silesia, the red-sandstone contains the formation zechstein; for the limestone of Runzendorf, filled with impressions of fishes, and analogous to the bituminous marl, abounding in fishes, of Thuringia, is entirely developed in the coal-formation. (Buch, Beob. vol. i. p. 104, 157; Id. Reisenach Norwegen, vol. i. 158; Raumer, Gebirge von Nieder-schlesien, p. 79). M. Boudant, Voy. Miner., vol. iii. p. 183., has observed a similar phenomenon in Hungary. In other districts, for example, in Switzerland, at the southern extremity of Saxony, the red-sandstone disappears entirely; because it is replaced, and, so to speak, overcome by a prodigious development of greywacke or of alpine limestone. (Friesleben, Kupfersch. p. 109). These effects of the alternation or unequal development of rock, are so much the more worthy of attention, that their study may throw light upon some apparent deviations from a generally acknowledged type of superposition, and that it may serve to a common type the series of position observed in very distant countries.

p.

In order to designate the formations composed of two rocks which alternate with another, I have generally preferred the words granite and gneiss, syenite and greenstone, to the more commonly adopted expressions of granite-gneiss, syenite-greenstone. I was apprehensive that this last method of designating formations composed of alternating rocks, might rather give rise to the idea of a passage from granite to gneiss, from syenite to greenstone. In fact, a geognost, whose works upon the trachytes of Germany have not been sufficiently appreciated, M. Nose, has already made use of the words graniteporphyries and porphyry-granites, to indicate varieties of structure and aspect, to separate the porphyritic granites from porphyries, which, from the frequency of crystals imbedded in the mass, presents an aggregational, a true granitic structure. By adopting the denominations of granite and gneiss, of syenite and porphyry, of greywacke and porphyry, of limestone and clay-slate, no doubt is left regarding the nature of the complex terms of the geognostical series.*

M. Humboldt next proceeds to consider the natural history of fossil organic remains, as connected with formations.

ART. XVI.—Extracts from an Analysis of the Transactions of the Royal Society of Edinburgh, vol. x. part 1, in the Edinburgh Philosophical Journal, April, 1824.

THE part of the Edinburgh Transactions which has just appeared, contains fifteen papers, illustrated by nine plates. The following brief analysis of these papers, with their titles, will convey to our readers some idea of their contents.

1. On the Existence of Two New Fluids in the Cavities of Minerals, which are immiscible, and possess remarkable Physical Proper ties. By DAVID BREWSTER, LL. D. F. R. S. Lond. and Sec. R. S. Edin.-P. 1—41.

In the preceding Numbers of this Journal, we have already given an abstract of the first seven sections of this paper. In the 8th section, which treats of the phenomena of a single fluid

* Translated from Essai Geognostique par Baron Alexandre de Humboldt.