Εικόνες σελίδας
PDF

breceia, which we have just regarded as an island in the ancient gulph, is covered with a thick forest of columnar cactus and opuntia, some thirty or forty feet high, covered with lichens, and divided into several branches in the form of candelabras, wearing a singular appearance. Near Maniquarez, and Punta Araya, we measured a cactus, the trunk of which was four feet nine inches in circumference. The European, acquainted only with the opuntia in our hothouses, is surprised to see the wood of this plant become so hard from age, that it resists for centuries both air and water, and that the Indians of Cumana employ it in preference for hords and doorposts. Cumana, Coro, the island of Margaretta, and Curacao, are the places in South America that abound most in the plants of the family of the nopals. There, only, a botanist can compose a monography of the genus cactus, the species of which vary not only in their flowers and fruits, but in the form of their articulated stem, the number of costae, and the disposition of the thorns: the divisions of property are marked by hedges formed of the agave and cactus. At San Fernando, S.A., the soil abounds in aquatic plants with sagittate leaves, and he remarks that some of these succulent plants are from eight to ten feet high. In Europe their assemblage would be considered a little wood.’ He also mentions a kind of bamboo which the Indians call jagua, which is found near San Fernando, more than forty feet in height. These, he observes, cannot but remind the admirer of fossils of the vast fossil bamboos which are found in the sandstones accompanying coal. Speaking of a rock of considerable height and magnitude, he observes, “Euphorbium, cacalia, kleinia, and cactus, which are become wild in the Canary Islands, as well as in the south of Europe and the whole continent of Africa, are the only plants we see on this arid rock, being plants which draw their nourishment rather from the air than from the soil in which they grow.’ He also remarks, “it is not, in general, by mosses and lichens that vegetation in the countries near the tropics begins. In the Canary Islands, as well as in Guinea and in the rocky coasts of Peru, the first vegetables that prepare the mould for others are the succulent plants.' We now follow Mr. Parkinson's description of I. CALCAREous VEGETABLE Fossils.—Lime is not very frequently the mineralising matter of vegetable fossils; it is however sometimes found introduced into the remains of wood in the form of spar, and sometimes it becomes, in the form of limestone, the internal substance of fossil reeds and of various succulent plants. 1. Calcareous spathose wood previously decayed.—Color light brown, surface rough and dull, but susceptible of polish; fracture dull, uneven, and rather spicular; interstices filled with nearly colorless spar. The line being removed from this fossil, by muriatic acid, a considerable portion of light-colored flocculent substance is deposited. Found in alluvia and in the oolite formation. 2. Calcareous spathose wood previously bitumimisca.—Color darkish red brown; surface commonly rough, but partially glossy; fracture dull,

uneven, and rather spicular, veined with spar of a lightish brown color. Found in the clay of bituminous slate accompanying the lias. The lime being removed, by the muriatic acid, a considerable volume of dark brown powder remains, which, when dried, is remarkably combustible, burning with a flame resembling that of some of the pyrophori. On the brown spar being subjected to the action of diluted muriatic acid, the bituminous matter with which it is colored rises in a film to the surface of the solution. The polished surface of both these fossils being examined with a lens, the spathose substance is seen to have permeated the minutest woody fibres in all their directions. The powder deposited during the solution of both these fossils is undoubtedly the woody fibre reduced to this state of minute division, in consequence of its penetration in every directiou by the spathose crystallisation. II. SILIceous VEGETABLE Fossils.-Themineralisation of vegetable substances is most frequently effected by those impregnations in which silex is the principal constituent; the fossils thus formed being remarkable for the correctness with which their forms and markings have been preserved. 1. Siliceous wood.—Its coloris generally grayish and yellowish white, thence passing into ash gray, grayish black, and different shades of brown. Its internal lustre is glistening, its fracture more or less perfect conchoidal, showing the ligneous texture. The fragments sharp-edged and translucent. It is harder than opal, and easily frangible. It is found in many parts of the world, but some of the finest specimens are obtained in the neighbourhood of Schemnitz and at Telkabanya in Hungary. It is frequently found in this island in the diluvian detritus, and in almost the whole of the green sand formation. Very large fragments are found in the Portland stones, the interstices of which are often beautifully sprinkled with quartz crystals. Interesting specimens are also discovered in the gritstone of the same formation in the blackdown pits of Devonshire, which are frequently rendered very interesting by the delicate amianthine form in which the silex is disposed. Specimens are also found in the sands of Bedfordshire. It is but rarely found in chalk; it however forms the nucleus of a flint nodule which is said to have been obtained in Berkshire. The varieties of siliceous wood depend not only on the nature of the combinations forming the lapideous matter of which it is chiefly constituted, but also, as has been already observed, on the state of the wood previous to its petrifaction. When the fossil is light colored, and of a shivery texture, the wood may be presumed to have been previously in a decayed state, or, as it is termed, rotten wood; and when close, compact, and dark-colored, it may have suffered previous bituminisation. A. Chalchedonic wood—In the most common form in which this variety appears, the color is of a yellowish-white, the substance resembling that of withered wood. The surface rough and

splintery, the splinters frequently so minute as to be wafted with the slightest breath. The internal part solid, chiefly formed of the translucent siliceous matter, which fills the interstices and such cavities as may have been formed by the teredines and other insects, and also sometimes invests the ends of the specimen in a mammillated or stalagmitic form. Specimens occur in which previous bituminisation also appears to have taken place, and in which the clear siliceous substance appears as if it had transuded into the cavities, and had exuded at the ends of the specimens. Hither must be referred those amorphous specimens which possess a rough surface, scarcely any lustre, with patches of apple-green color and of a quartzose hardness, intermixed with others of a light or light gray color, considerably softer. When cut and polished, the white parts display evident marks of vegetable texture; either that of very fine grained woods, or of some of the palms or reeds, the spaces between being filled with siliceous matter, either translucent or of an apple-green color. B. Jasperine wood displays all the colors and appearances belonging to common jasper, so disposed as to mark the existence of ligneous texture, and frequently so varied as to give the resemblance of different woods. It is usually opaque, but sometimes translucent at the edges, and sometimes in patches, where it appears as jasper agate. Its fracture passes from conchoidal to flat and earthy; its internal lustre is generally dull, but sometimes approaching to resinous; its interstices are frequently set with minute crystals. The texture of the wood is discoverable in some very rare specimens of heliotrope, or bloodstone. C. Opaline wood occurs in pieces of a yellowish or yellowish-white color, passing into different shades of brown: surface generally marked by the ligneous structure, and possessing a resinous lustre. The fracture more or less approaching to perfect conchoidal, showing the ligneous marking and a glistening lustre. Fragments sharp-edged, and somewhat translucent: the surface sometimes dull, like wood, and the internal substance transparent. It is considered by Dr. Thomson as consisting of wood penetrated by opal, and as being so intimately connected with opal that it would perhaps be better to unite them. D. Pitchstone wood—Specimens of fossil

wood, evidently showing its original texture, and

answering to the characters of pitchstone, are frequently seen: its colors are yellow, brown, reddish brown, red, black, white, and gray, with various intermediate shades; fracture is flattish, imperfectly large conchoidal; lustre varying between dull, vitreous, and resinous. The woody texture is to be traced also in numerous lapideous substances bearing the intermingled characters of pitchstone, opal, jasper, chalcedony, jasper-agate, &c. III. Aluminous VEGETABLE Fossils. 1. Bituminous slate, schistus, and shale, containing vegetable remains, are frequently met with in the neighbourhood of coal. These remains, as have been already mentioned, are of various gramina, cryptogami, and succulent plants. On allowing some of these bodies to remain in water,

their substance becomes softened down, ind is resolved into a mass in which the vegetaole matter is obvious. 2. Aluminous wood.—The wood which has been thus named by different authors, by its proneness to combustion, and by the other prop. which they describe it to possess, should e considered as pyritous wood, having obtained its change in the ferruginous clay in which it has been imbedded. The mineralising matter of metallic fossil vegetables is most commonly the pyrites or sulphurets and carbonates of iron, o zinc, or lead. . FERRUGINous Fossil Wood. 1. Pyritical—In this fossil the sulphuret of iron pervades the charcoal into which the vegetable matter has been converted. When first found it generally possesses metallic brilliancy, is sufficiently hard to scratch glass, emits sparks on collision with steel, and displays the forms and markings pointing out its vegetable origin; but it soon begins to suffer from decomposition, when its characters change, and it finally resolves into a saline flocculent substance. 2. Carbonated.—In these specimens, which are of different shades of brown color, and generally of a uniform substance, the marks of the vegetable origin are easily observable, although not so distinct as in the specimens of the preceding species before the commencement of the decomposition. II. FERRUG Inous Fossil Seeds, &c. Innumerable seeds, seed-vessels, &c., have been found by Mr. Crow and others, in the blue clay of Sheppey in the state of pyrites. Most of these belong to plants unknown to our botanists; the existing plants, to which the others seem to o, are some of those of the warmer climates. III. CUPREous Fossil WooD. 1. Pyritical.—This fossil is distinguishable from the ferruginous pyritical wood, by the py

rites being of rather a darker color, but chiefly

by the blue, or green color which partially pervades the fossil. In some specimens, in which the general appearance is that of bituminous wood, the metallic impregnation can only be detected by the weight of the fossil and the blue or green hue on its surface. 2. Wood converted into carbonate and hydrate of copper.—Cupreous wood in this state forms very beautiful specimens, displaying, not only on its surface, but in its substance, mingled with the charred wood, the most vivid blue and green colors, with patches of the carbonate in the state of malachite. The finest specimens of cupreous wood are obtained from the copper mines of Siberia. 3. Wood mineralised by lead.—Specimens of wood containing galena, the sulphuret of lead, have been chiefly discovered in Derbyshire. The leaves of plants, except those of gramina, junci, and of the cryptogamia, are seldom found in a mineralised state. The lobes and pinnulae of ferns, as has been before mentioned, are frequently found in a bituminised state in nodules of ironstone, and in immense quantities with the remains of gramina and succulent plants in the schistose and slaty coverings of coal.

Among the numerous remains of plants very few are found which agree in their specific characters with any known species, and many indeed differ so much as to render it difficult to determine even the genus under which they should be placed. The leaves of trees are only found -in substances which appear to be of modern formation. Among these are said to have been found those of the willow, the pear-tree, mulberry-tree, and of several others. These have been found in fossil calcareous stone, chiefly in that of Oeningen, and in the calcareous tufa bordering those lakes and rivers which abound in calcareous matter. Leaves are sometimes found in sandstone which somewhat resemble those of trees, but which most probably have belonged to aquatic plants. In the gray chalk, small white ramose forms are found, which pervade the chalk, and have the appearance of being of vegetable origin. Wood and other vegetable substances are frequently found in clay and limestone in the state of charcoal. It cannot always be ascertained by what means this change has been effected; but in that which is found in the blue clay, and in other situations in which pyrites prevail, the change may safely be attributed to the decomposition of the pyrites with which those substances had been impregnated.

Mosses, Conferva, &c.—Rounded }. called moss agates, are frequently found on the coast of the North Riding of Yorkshire; and Dr. M’Culloch describes them as having been found on the shore at Dunglas in Scotland, containing substances which have the appearance of vegetables.

Daubenton and Blumenbach had expressed their conviction of the vegetable origin of these substances; still many considered them as entirely mineral : but Dr. M'Culloch, pursuing this enquiry with his usual zeal and acuteness, observes, that deception is very likely to arise in these specimens, from the well known metallic arborizations emulating the vegetable forms, becoming blended with the real vegetable; and from the actual investment of the whole plant with carbonate of iron; but the most common source of deception and obscurity, in the Dr.'s opinion, “will be found in the whimsical and fibrous disposition occasionally assumed by chlorite, its color often imitating the natural hue of a plant as perfectly as its fibrous and ramified appearance does the disposition and form of one.’ All the plants that have been discovered in this state of envelopment in quartz appear to belong to certain species of the cryptogamia class, chiefly byssi, confervae, jungermanniae, and the mosses. The stones found at Dunglas, Dr. M'Culloch observes, ‘contain remains of organized substances of an epocha at least equally ancient with that in which the vegetable remains found in the floetz strata existed. As the species ascertained by Daubenton have, in all probability, been preserved in recent formations of chalcedony, so the Dr. thinks that “those which he describes have been preserved in the chalcedonies of former days.” The moss agates of the Yorkshire coast appear to be of the ancient, whilst other specimens prove the correctness of Dr. M'Culloch's opinion, that some of these fossils are of recent formation.

The remarks of Dr. M'Culloch on the mode in which these curious investments were accom.plished, deserve particular attention:—“The remains are, in fact (if I may use such an expression), embalmed alive. To produce this effect, we can only conceive a solution of silex in water, so dense as to support the weight of the substance involved, a solution capable of solidifying in a short space of time, or capable at least of suddenly gelatinizing previously to the ultimate change by which it became solidified into stone.’ Dr. M'Culloch describes and figures a congeries of tubuli contained in an oriental agate: similar substances are found in the pebbles on the Yorkshire coast.

A knowledge of the vegetable fossils peculiar to the different strata will, in all probability, open to us considerable stores of instruction; we may thereby learn, not only the nature of the several vegetable beings of the earlier ages of this planet, but may ascertain the order in which the several tribes were created: and, reckoning upon the considerable advance which has been made in our knowledge of the structure of the earth, and upon the eagerness with which enquiries respecting the organic remains of former periods are pursued, the attainment of such knowledge, it may be presumed, is not far distant. At present we know of no vegetable remains of earlier existence than those which belong to the coal formation; and these appear to be chiefly derivad from various grasses and reeds, and plants of the cryptogamous and succulent tribes, many of which are not known to exist on the surface of the earth at present. From the latter of these the coal itself appears to have chiefly proceeded. In the mountain limestone above the coal, and in the different members of this formation existing between this and the blue lias, vegetable remains appear to be of but rare occurrence; so that particulars of such as have been discovered in these situations may furnish much useful information, and especially with respect to those fossils which are supposed to have derived their origin from wood. . It has been assumed that wood, or parts of trees, have been found in coal and in the accompanying coal-measures, but some confirmation of these accounts seems to be required. The description of these fossils has seldom been so particular and exact as to yield positive evidence of their original nature; and, as has been already shown, the instances are by no means infrequent in which the traces, and even the remains, of cactuses and other succulent plants, had given rise to the belief of the existence of fossil trees in these strata. This opinion may therefore have obtained seeming confirmation from the ligneous hardness which large plants of this kind might have acquired, and which, perhaps, might be traced in their mineralised remains. The earliest

stratification in which fossil wood exists is not

perhaps at present determined; but it seems that the earliest appearance in this island of fossil wood, which by its uniformity of character appears to belong to a particular bed, is the spathose bituminous wood of the blue lias, as found at Lyme in Dorsetshire, and in the neighbourhood of Bath. In the next formation, and o: in that of the green sand, siliceous ossil wood occurs frequently. Very delicate specimens are found in the sandstone, the whetstone of the Blackdown hills of Devonshire. The specimens of fossil wood found in the Portland stone are frequently of very considerable size, and bear all the characteristic marks of wood: these are also siliceous, and are often beautifully sprinkled on their interior surfaces with quartz crystals. Siliceous fossil wood is also found in other situations, as in the sands of Wooburn in Bedfordshire: it also occurs at Folkstone in Kent, in that part of the green sand where it approximates to the superincumbent marl, in which it is also found. Traces of wood are hardly ever discovered in the chalk itself, and so rarely in the accompanying flint nodules, that the knowledge of but one specimen, an instance of this 9ccurrence, is known to the writer of these pages. But in the blue clay, incumbent upon this immense accumulation of chalk, fossil wood, pierced with teredines, and impregnated with calcareous spar, is exceedingly abundant: and in almost every sunken part of this bed, and even of the whole surface of this island, the remains are discoverable of vast forests which have suffered little other change than that of having undergone different degrees of bituminisation. By these facts, concludes Mr. Parkinson, we learn that, at some very remote and early period of the existence of this planet, it must have abounded with plants of the succulent kind, and, as it appears from their remains, in great variety of form and luxuriancy of size These, from what is discoverable of their structure, beset with setae and spines, were not formed for the food of animals; nor, from the nature of the substances of which they were composed, were they fitted to be applied to the various purposes to which wood, the product of the earth at a subsequent Period, has been found to be so excellently adapted, by man. Their remains, it must also be remarked, are now found in conjunction with that substance which nature has, in all probability, formed from them; and which, by the peculiar economical modification of its combustibility, is rendered an invaluable article of fuel. If this be admitted to be the origin of coal, a satisfactory cause will appear for the vast abundance of vegetable matter with which the earth must have been stored in its early ages: this vast, and in any other view useless, creation, will thus be ascertained to have been a beneficent arrangement by Providence for man, the being of a creation of a later period.

Class IX-HOMO.

Remains of the human species are not found n secondary strata; but in the clay of the fissures of rocks they are not infrequent, and they have been found in alluvial soil at Koestretz in Germany. Mr. Konig's account of the most celebrated fossile skeleton yet discovered (and which is now in the British Museum) is thus introduced :

“All the circumstances under which the known depositions of bones occur,' says this gentleman, “both in alluvial beds and in the caverns and fissures of floetz limestone tend to prove, that

the animals to which they belonged met their fate in the very places where they now lie buried. Hence it may be considered as an axiom, that man, and other animals, whose bones are not found intermixed with them, did not coexist in time and place. The same mode of reasoning would further justify us in the conclusion, that, if those catastrophes which overwhelmed a great proportion of the brute creation were general, as geognostic observations in various parts of the world render probable, the creation of man must have been posterior to that of those genera and species of mammalia which perished by a general cataclysm, and whose bones are so thickly disseminated in the more recent formations of rocks. “The human skeletons from Guadaloupe are called Galibi by the natives of that island; a name said to have been that of an ancient tribe of Caribs of Guiana, but which, according to a plausible conjecture, originated in the substitution of the letter l instead of r, in the word Caribbee. No mention is made of them by any author except general Ernouf, in a letter to M. Faujas St. Fond, inserted in vol v. 1805 of the Annales du Muséum; and by M. Lavaisse, in his Voyage à la Trinidad, &c., published in 1813. The former of these gentlemen writes, that, on that part of the windward side of the Grande-Terre called La Moûle, skeletons are found enveloped in what he terms ‘Masses de madrépores pétrifiés,' which being very hard, and situated within the line of high water, could not be worked without great difficulty, but that he expected to succeed in causing some of these masses to be detached, the measurements of which he states to be about eight feet by two and a half. “The block brought home by Sir Alexander Cochrane exactly answered this account with regard to the measurements; in thickness it was about a foot and a half. It weighed nearly two tons; its shape was irregular, approaching to a flattened oval, with here and there some concavities, the largest of which, as it afterwards appeared, occupying the place where the thigh bone had been situated, the lower part of which was therefore wanting. Except the few holes evidently made to assist in raising the block, the masons here declared, that there was no mark of a tool upon any part of it; and, indeed, the whole had very much the appearance of a huge nodule disengaged from a surrounding mass. The situation of the skeleton in the block was so superficial, that its presence in the rock on the coast had probably been indicated by the projection of some of the more elevated parts of the left fore-arm. . “The skull is wanting; a circumstance which is the more to be regretted as this characteristic part might possibly have thrown some light on the subject under consideration, or would, at least, have settled the question, whether the skeleton is that of a Carib, who used to give the frontal bone of the head a particular shape by compression; which had the effect of depressing the upper, and protruding the lower edge of the orbits, so as to make the direction of their opening nearly upwards, or horizontal, instead

AT

of vertical. The vertebrae of the neck were lost with the head. The bones of the thorax bear all the marks of considerable concussion, and are completely dislocated. The seven true ribs of the left side, though their heads are not in connexion with the vertebrae, are complete; but only three of the false ribs are observable. On the right side only fragments of these bones are seen; but the upper part of the seven true ribs of this side are found on the left, and might at first sight be taken for the termination of the left ribs. The right ribs must therefore have been violently broken, and carried over to the left side, where, if this mode of viewing the subject be correct, the sternum must likewise lie concealed below the termination of the ribs. The small bone dependent above the upper ribs of the left side appears to be the right clavicle. The right os humeri is lost; of the left nothing remains except the condyles in connexion with the fore-arm, which is in the state of pronation; the radius of this side exists nearly in its full length, while of the ulna the lower part only remains, which is considerably pushed upwards. Of the two bones of the right fore-arm the inferior terminations are seen. Both the rows of the bones of the wrists are lost, but the whole metacarpus of the left hand is displayed, together with part of the bones of the fingers: the first joint of the fore finger rests on the upper ridge of the os pubis, the two others, detached from their metacarpal bones, are propelled downwards, and situated at the inner side of the femur, and below the foramen magnum ischii of this side. Vestiges of three of the fingers of the right hand are likewise visible, considerably below the 1ower portion of the fore-arm, and close to the upper extremity of the femur. The vertebrae may be traced along the whole length of the column, but are in no part of it well defined. Of the os sacrum the superior portion only is distinct: it is disunited from the last vertebra and the ilium, and driven upwards. The left os ilium is nearly complete; but shattered, and one of the fragments depressed below the level of the rest: the ossa pubis, though well defined, are gradually lost in the mass of the stone. On the right side the os innominatum is completely shattered, and the fragments are sunk; but, towards the acetabulum, part of its internal cellular structure is discernible. “The thigh bones and the bones of the leg of the right side are in good preservation, but, being considerably turned outwards, the fibula lies buried in the stone, and is not seen. The lower part of the femur of this side is indicated only by a bony outline, and appears to have been distended by the compact limestone that fills the cavities both of the bones of the leg and thigh, and to the expansion of which these bones R. owe their present shattered condition. he lower end of the left thigh bone appears to have been broken and lost in the operation of detaching the block; the two bones of the leg, however, on this side are nearly complete: the tibia was split almost the whole of its length a little below the external edge, and the fissure, being filled up with limestone, now presents

itself as a dark colored straight line. The portion of the stone which contained part of the bones of the tarsus and metatarsus was unfortunately broken; but the separate fragments are preserved. “The whole of the bones, when first laid bare, had a mouldering appearance, and the hard surrounding stone could not be detached, without frequently injuring their surface; but, after an exposure for some days to the air, they acquired a considerable degree of hardness. Sir H. Davy, who subjected a small portion of them to chemical analysis, found that they contained part of their animal matter, and all their phosphate of lime. Here follows an exact description of the rock, in which the fossile skeleton is found. The attention of geologists being now directed towards this object, it may be expected that a scientific examination of the circumstances under which this limestone occurs will not fail ere long to fix its age, and assign to it the place it is to occupy in the series of rocks. All our present information respecting the Grande Terre of Guadaloupe amounts to this, that it is a flat limestone country, derived principally from the detritus of zoophytes, with here and there single hills (mornes) composed of shell limestone ; while Guadaloupe, properly so called, separated from the upper part by a narrow channel of the sea, has no traces of limestone, and is entirely volcanic.’ See plate II. fig. 3. Since the above has been prepared we have happened of the accounts of an old acquaintance, Mr. Trimmer, of some organic remains found near Brentford, Middlesex; the spot mentioned will be familiar to many of our readers. He is describing in order the remains of two fields, not contiguous. “The first, he says, “is about half a mile north of the Thames at Kew Bridge; its surface is about twenty-five feet above the Thames at low water. The strata here are, first, sandy loam from six to seven feet, the lowest two feet slightly calcareous. Secondly, sandy gravel, a few inches only in thickness. Thirdly, loam slightly calcareous, from one to five feet: between this and the next stratum peat frequently intervenes is small patches, of only a few yards wide and a few inches thick. Fourthly, gravel containing water; this stratum varies from two to ten feet in thickness, and is always the deepest in the places covered by peat; in these places the lower part of the stratum becomes an heterogeneous mass of clay, sand, and gravel, and frequently exhales a disagreeable muddy smell. Fifthly, the main stratum of blue clay, which lies under this, extends under London and its vicinity; the average depth of this clay has been ascertained, by wells that have been dug through it, to be about 200 feet under the surface of the more level lands, and proportionally deeper under the hills, as appears from lord Spencer's well, at Wimbledon, which is 567 feet deep. This stratum, besides figured fossils, contains pyrites and many detached nodules; at the depth of twenty feet there is a regular stratum of these nodules, some of which are of very considerable size. “In the first stratum, as far as my observatio

« ΠροηγούμενηΣυνέχεια »