These recent formations, so rich in vestiges of organized bodies, furnish a vast field of observation to those who are familiar with the zoological character of rocks. To examine these vestiges in strata superposed as by steps, one above another, is to study the Fauna of different ages and to compare them together. The geography of animals marks out limits in space, according to the diversity of climates, which determine the actual state of vegetation on our planet. The geology of organized bodies, on the contrary, is a fragment of the history of nature, taking the word history in its proper acceptation: it describes the inhabitants of the earth according to succession of time. We may study genera and species in museums, but the Fauna of different ages, the predominance of certain shells, the numerical relations which characterize the animal kingdom and the vegetation of a place or of a period, should be studied in sight of those formations. It has long appeared to me that in the tropics as well as in the temperate zone the species of univalve shells are much more numerous than bivalves. From this superiority in number the organic fossil world furnishes, in every latitude, a further analogy with the intertropical shells that now live at the bottom of the ocean. In fact, M. Defrance, in a work* full of new and ingenious ideas, not only recognizes this preponderance of the univalves in the number of the species, but also observes that out of 5500 fossil univalve, bivalve and multivalve shells, contained in his rich collections, there are 3066 univalve, 2108 bivalve, and 326 multivalve; the univalve fossils are therefore to the bivalve as three to two. (* Table of Organized Fossil Bodies, 1824.)

13. FORMATION OF PYROXENIC AMYGDALOID AND PHONOLITE, BETWEEN ORTIZ AND CERRO DE FLORES.

I place pyroxenic amygdaloid and phonolite (porphyrschiefer) at the end of the formations of Venezuela, not as being the only rocks which I consider as pyrogenous, but as those of which the volcanic origin is probably posterior to the tertiary strata. This conclusion is not deduced from the observations I made at the southern declivity of the littoral Cordillera, between the Morros of San Juan, Parapara and the Llanos of Calabozo. In that region local circumstances would possibly lead us to regard the amygdaloids of Ortiz as linked to a system of transition rocks (amphibolic serpentine, diorite, and carburetted slate of Malpasso); but the eruption of the trachytes across rocks posterior to the chalk (in the Euganean Mountains and other parts of Europe) joined to the phenomenon of total absence of fragments of pyroxenic porphyry, trachyte, basalt and phonolite (The fragments of these rocks appear only in tufas or conglomerates which belong essentially to basaltic formations or surround the most recent volcanoes. Every volcanic formation is enveloped in breccia, which is the effect of the eruption itself.), in the conglomerates or fragmentary rocks anterior to the recent tertiary strata, renders it probable that the appearance of trap rocks at the surface of the earth is the effect of one of the last revolutions of our planet, even where the eruption has taken place by crevices (veins) which cross gneiss-granite, or the transition rocks not covered by secondary and tertiary formations.

The small volcanic stratum of Ortiz (latitude 9 degrees 28 minutes to 9 degrees 36 minutes) formed the ancient shore of the vast basin of the Llanos of Venezuela: it is composed on the points where I could examine it of only two kinds of rocks, namely, amygdaloid and phonolite. The greyish blue amygdaloid contains fendilated crystals of pyroxene and mesotype. It forms balls with concentric layers of which the flattened centre is nearly as hard as basalt. Neither olivine nor amphibole can be distinguished. Before it shows itself as a separate stratum, rising in small conic hills, the amygdaloid seems to alternate by layers with the diorite, which we have mentioned above as mixed with carburetted slate and amphibolic serpentine. These close relations of rocks so different in appearance and so likely to embarrass the observer give great interest to the vicinity of Ortiz. If the masses of diorite and amygdaloid, which appear to us to be layers, are very large veins, they may be supposed to have been formed and upheaved simultaneously. We are now acquainted with two formations of amygdaloid; one, the most common, is subordinate to the basalt: the other, much more rare,* (* We find examples of the latter in Norway (Vardekullen, near Skeen), in the mountains of the Thuringerwald; in South Tyrol; at Hefeld in the Hartz, at Bolanos in Mexico etc.) belongs to the pyroxenic porphyry.* (* Black porphyries of M. von Buch.) The amygdaloid of Ortiz approaches, by its oryctognostic characters, to the former of those formations, and we are almost surprised to find it joining, not basalt, but phonolite,* an eminently felspathic rock, in which we find some crystals of amphibole, but pyroxene very rarely, and never any olivine. (* There are phonolites of basaltic strata (the most anciently known) and phonolites of trachytic strata (Andes of Mexico). The former are generally above the basalts; and the extraordinary development of felspar in that union, and the want of pyroxene, have always appeared to me very remarkable phenomena.) The Cerro de Flores is a hill covered with tabulary blocks of greenish grey phonolite, enclosing long crystals (not fendillated) of vitreous felspar, altogether analogous to the phonolite of Mittelgebirge. It is surrounded by pyroxenic amygdaloid; it would no doubt be seen below, issuing immediately from gneiss-granite, like the phonolite of Biliner Stein, in Bohemia, which contains fragments of gneiss embedded in its mass.

Does there exist in South America another group of rocks, which may be preferably designated by the name of volcanic rocks, and which are as distinct from the chain of the Andes, and advance as far towards the east as the group that bounds the steppes of Calabozo? Of this I doubt, at least in that part of the continent situated north of the Amazon. I have often directed attention to the absence of pyroxenic porphyry, trachyte, basalt and lavas (I range these formations according to their relative age) in the whole of America eastward of the Cordilleras. The existence even of trachyte has not yet been verified in the Sierra Nevada de Merida which links the Andes and the littoral chain of Venezuela. It would seem as if volcanic fire, after the formation of primitive rocks, could not pierce into eastern America. Possibly the scarcity of argentiferous veins observed in those countries may be owing to the absence of more recent volcanic phenomena. M. Eschwege saw at Brazil some layers (veins?) of diorite, but neither trachyte, basalt, dolerite, nor amygdaloid; and he was therefore much surprised to see, in the vicinity of Rio Janeiro, an insulated mass of phonolite, exactly similar to that of Bohemia, piercing through gneiss. I am inclined to believe that America, on the east of the Andes, would have burning volcanoes if, near the shore of Venezuela, Guiana and Brazil, the series of primitive rocks were broken by trachytes, for these, by their fendillation and open crevices, seem to establish that permanent communication between the surface of the soil and the interior of the globe, which is the indispensable condition of the existence of a volcano. If we direct our course from the coast of Paria by the gneiss-granite of the Silla of Caracas, the red sandstone of Barquisimeto and Tocuyo, the slaty mountains of the Sierra Nevada de Merida, and the eastern Cordillera of Cundinamarca to Popayan and Pasto, taking the direction of west-south-west, we find in the vicinity of those towns the first volcanic vents of the Andes still burning, those which are the most northerly of all South America; and it may be remarked that those craters are found where the Cordilleras begin to present trachytes, at a distance of eighteen or twenty-five leagues from the present coast of the Pacific Ocean.* (* I believe the first hypotheses respecting the relation between the burning of volcanoes and the proximity of the sea are contained in Aetna Dialogus, a very eloquent though little-known work by Cardinal Bembo.) Permanent communications, or at least communications frequently renewed, between the atmosphere and the interior of the globe, have been preserved only along that immense crevice on which the Cordilleras have been upheaved; but subterranean volcanic forces are not less active in eastern America, shaking the soil of the littoral Cordillera of Venezuela and of the Parime group. In describing the phenomena which accompanied the great earthquake of Caracas,* on the 26th March, 1812, I mentioned the detonations heard at different periods in the mountains (altogether granitic) of the Orinoco. (* I stated in another place the influence of that great catastrophe on the counter-revolution which the royalist party succeeded in bringing about at that time in Venezuela. It is impossible to conceive anything more curious than the negociation opened on the 5th of April, by the republican government, established at Valencia in the valleys of Aragua, with Archbishop Prat (Don Narciso Coll y Prat), to engage him to publish a pastoral letter calculated to tranquilize the people respecting the wrath of the deity. The Archbishop was permitted to say that this wrath was merited on account of the disorder of morals; but he was enjoined to declare positively that politics and systematic opinions on the new social order had nothing in common with it. Archbishop Prat lost his liberty after this singular correspondence.) The elastic forces which agitate the ground, the still-burning volcanoes, the hot sulphurous springs, sometimes containing fluoric acid, the presence of asphaltum and naphtha in primitive strata, all point to the interior of our planet, the high temperature of which is perceived even in mines of little depth, and which, from the times of Heraclitus of Ephesus, and Anaxagoras of Clazomenae, to the Plutonic theory of modern days, has been considered as the seat of all great disturbances of the globe.

The sketch I have just traced contains all the formations known in that part of Europe which has served as the type of positive geology. It is the fruit of sixteen months' labour, often interrupted by other occupations. Formations of quartzose porphyry, pyroxenic porphyry and trachyte, of grauwacke, muschelkalk and quadersandstein, which are frequent towards the west, have not yet been seen in Venezuela; but it may be also observed that in the system of secondary rocks of the old continent muschelkalk and quadersandstein are not always clearly developed, and are often, by the frequency of their marls, confounded with the lower layers of Jura limestone. The muschelkalk is almost a lias with encrinites; and quadersandstein (for there are doubtless many above the lias or limestone with gryphites) seems to me to represent the arenaceous layers of the lower shelves of Jura limestone.

I have thought it right to give at some length this geologic description of South America, not only on account of the novel interest which the study of the formations in the equinoctial regions is calculated to excite, but also on account of the honourable efforts which have recently been made in Europe to verify and extend the working of the mines in the Cordilleras of Columbia, Mexico, Chile and Buenos Ayres. Vast sums of money have been invested for the attainment of this useful end. In proportion as public confidence has enlarged and consolidated those enterprises, from which both continents may derive solid advantage, it becomes the duty of persons who have acquired a local knowledge of these countries to publish information calculated to create a just appreciation of the relative wealth and position of the mines in different parts of Spanish America. The success of a company for the working of mines, and that of works undertaken by the order of free governments, is far from depending solely on the improvement of the machines employed for draining off the water, and extracting the mineral, on the regular and economical distribution of the subterraneous works, or the improvements in preparation, amalgamation, and melting: success depends also on a thorough knowledge of the different superposed strata. The practice of the science of mining is closely linked with the progress of geology; and it would be easy to prove that many millions of piastres have been rashly expended in South America from complete ignorance of the nature of the formations, and the position of the rocks, in directing the preliminary researches. At the present time it is not precious metals solely which should fix the attention of new mining companies; the multiplication of steam-engines renders it indispensable, wherever wood is not abundant or easy of transport, to seek at the same time to discover coal and lignites. In this point of view the precise knowledge of the red sandstone, coal-sandstone, quadersandstein and molassus (tertiary formation of lignites), often covered with basalt and dolerite, is of great practical importance. It is difficult for a European miner, recently arrived, to judge of a country presenting so novel an aspect, and when the same formations cover an immense extent. I hope that the present work, as well as my Political Essay on New Spain, and my work on the Position of Rocks in the Two Hemispheres, will contribute to diminish those obstacles. They may be said to contain the earliest geologic information respecting places whose subterraneous wealth attracts the attention of commercial nations; and they will assist in the classification of the more precise notions which later researches may add to my labours.

The republic of Colombia, in its present limits, furnishes a vast field for the enterprising spirit of the miner. Gold, platinum, silver, mercury, copper, gem-salt, sulphur and alum may become objects of important workings. The production of gold alone amounted, before the outbreak of the political dissensions, on the average, to 4700 kilogrammes (20,500 marks of Castile) per annum. This is nearly half the quantity furnished by all Spanish America, a quantity which has an influence the more powerful on the variable proportions between the value of gold and silver, as the extraction of the former metal has diminished at Brazil, for forty years past, with surprising rapidity. The quint (a tax which the government raises on gold-washings) which in the Capitania of Minas Geraes was, in 1756, 1761 and 1767, from 118, 102 and 85 arobas of gold (of 14 3/5 kilogrammes), has fallen, during 1800, 1813 and 1818, to 30, 20 and 9 arobas; an arob of gold having, at Rio Janeiro, the value of 15,000 cruzados. According to these estimates the produce of gold in Brazil, making deductions for fraudulent exportation, was, in the middle of the eighteenth century, the years of the greatest prosperity of the gold-washings, 6600 kilogrammes, and in our days, from 1817 to 1820, 600 kilogrammes less. In the province of San Paulo the extraction of gold has entirely ceased; in the province of Goyaz, it was 803 kilogrammes in 1793 and in 1819 scarcely 75. In the province of Mato Grosso it is almost nothing; and M. Eschwege is of opinion that the whole produce of gold in Brazil does not amount at present to more than 600,000 cruzados (scarcely 440 kilogrammes). I dwell on these particulars because, in confounding the different periods of the riches and poverty of the gold-washings of Brazil, it is still affirmed in works treating of the commerce of the precious metals, that a quantity of gold equivalent to four millions of piastres (5800 kilogrammes of gold*) flows into Europe annually from Portuguese America. (* This error is twofold: it is probable that Brazilian gold, paying the quint, has not, during the last forty years, risen to 5500 kilogrammes. I heretofore shared this error in common with writers on political economy, in admitting that the quint in 1810 was still (instead of 26 arrobas or 379 kilogrammes) 51,200 Portuguese ounces, or 1433 kilogrammes; which supposed a product of 7165 kilogrammes. The very correct information afforded by two Portuguese manuscripts on the gold-washings of Minas Geraes, Minas Novas and Goyaz, in the Bullion Report for the House of Commons, 1810, acc. page 29, goes as far only as 1794, when the quinto do ouro of Brazil was 53 arrobas, which indicates a produce of more than 3900 kilogrammes paying the quint. In Mr. Tooke's important work, On High and Low Prices part 2 page 2) this produce is still estimated (mean year 1810 to 1821) at 1,736,000 piastres; while, according to official documents in my possession, the average of the quint of those ten years amounted only to 15 arrobas, or a product quint of 1095 kilogrammes, or 755,000 piastres. Mr. John Allen reminded the Committee of the Bullion Report, in his Critical Notes on the table of M. Brongniart, that the decrease of the produce of the gold-washings of Brazil had been extremely rapid since 1794; and the notions given by M. Auguste de Saint Hilaire indicate the same desertion of the gold-mines of Brazil. Those who were miners have become cultivators. The value of an arroba of gold is 15,000 Brazilian cruzados (each cruzado being 50 sous). According to M. Franzini the Portuguese onca is equal to 0.028 of a kilogramme, and 8 oncas make 1 mark; 2 marks make 1 arratel, and 32 arratels 1 arroba.) If, in commercial value, gold in grains prevails, in the republic of Columbia, over the value of other metals, the latter are not on that account less worthy to fix the attention of government and of individuals. The argentiferous mines of Santa Anna, Manta, Santo Christo de las Laxas, Pamplona, Sapo and La Vega de Sapia afford great hope. The facility of the communications between the coast of Columbia and that of Europe imparts the same interest to the copper-mines of Venezuela and New Grenada. Metals are a merchandize purchased at the price of labour and an advance of capital; thus forming in the countries where they are produced a portion of commercial wealth; while their extraction gives an impetus to industry in the most barren and mountainous districts.

INDEX.

Acephali.