« AnteriorContinuar »
nally invisible or but faintly distinguishable, when the glass had been for some time exposed to a low heat in the flue of the annealing oven. Had this specimen been kept long enough in the hot flue, it would eventually have become altogether devitrified or converted into a crystalline stony mass (Réaumur's porcelain), in which, however, the parallel structure due to the striæ of fusion can still be distinguished either by the naked eye or under the microscope, owing to the general direction and parallelism of the longer axes of the crystals which compose the mass.
What is thus artificially produced on the small scale can be seen on the large scale in nature in obsidian and other glassy lavas; and in most volcanic countries hand specimens can be obtained showing all the stages, exactly as in the case of glass. The crystals of the mineral components of the lavas appear first along the lines of striation, and go on forming until the whole mass has become devitrified and is entirely crystalline, and resembles Pl. LXXIII., fig. 9, which represents a hand specimen from the apparently bedded and intercalated lavas (which form so peculiar a feature of this part of South America) near the river Mauri, where it forms the boundaryline between the republics of Peru and Bolivia. In this specimen the rock has lost all trace of its originally glassy or vitreous appearance, and having become completely devitrified, is seen to consist mainly of felspar crystals along with a little augite, quartz and an occasional plate of mica (a trachydolorite); yet, as is seen in the figure, a distinct parallel structure (due to the striæ of fusion) is still preserved in the rock, which, being the lines of least resistance in it, renders it much more fissile in this direction than across the grain, exactly as is commonly found to be the case in a normal or metamorphosed rock of true sedimentary origin : in fact, some of these rocks, which underlie conformably oolitic and other strata of still later age, and which show themselves for miles intercalated conformably in the strata, have been mistaken for true sedimentary beds, and in one instance described as sandstone (which never could have occurred had their mineral nature been examined, although they are easily traced to the active volcanoes in the vicinity from which they have been emitted. Even when such rocks are found to be extremely fine-grained in texture, the parallel structure due to pre-existing striation, although often very difficult to distinguish on the rough surface of fresh fracture, is commonly found to show itself very distinctly on the surface of the rock when weathered.
Any geologist who has had the opportunity of studying such rocks in the field, cannot but consider it probable that the socalled granitic gneiss or gneiss granites owe their structure to milar causes.
In concluding these remarks on the different classes of parallel structure met with in rock masses in nature, the author would but state that his main object has been to direct the special attention of geologists working in the field to the extreme importance of studying carefully, not only the external contours, but the internal structure of rock masses also, in order thereby to avoid the mistakes which have been frequently committed; such as recording as stratification planes which are in reality due to the effects of joints, cleavage, or foliation, or describing rocks of truly intrusive or eruptive nature as of sedimentary origin.
THE lion, mammoth and reindeer, have already been dis
I cussed from the point of view offered by palæontology and archæology. In the present essay I intend to treat of the value of bears and wolves in classification, and to see how far they throw light on the ancient physical condition of Britain. In the latter respect we shall find that they offer testimony to the state of things, which is of no small importance to the student of early English and mediæval history, while in the former they compel us to analyse M. Lartet's method of subdividing the quaternary period.
The genus bear has not been discovered in any deposits of greater antiquity than the pleiocene age, and is represented in Europe by many extinct species and several existing varieties. The British species are four in number: the bear of Auvergne, the cave and grizzly, and the common brown or black bear. Each species has its own peculiar range, both in space and in time. The first, or the Ursus Arvernensis—the remains of which are preserved in the magnificent collections from the forest-bed of Norfolk made by the Rev. J. Gunn and the late Rev. S. W. King—was a creature of about the same size as the common European species, and armed with canines which are quite puny in comparison with those of the Ursus spelaus. It has not yet been figured or described as a British species, and its remains are very rare. On the Continent, however, it is, as Dr. Falconer remarks, abundantly found in the pleiocenes of Auvergne and of the Val d'Arno. It has not yet been found in any of the German pleiocenes, nor in any strata younger than the preglacial forest-bed of Norfolk. We may therefore view it as a pleiocene carnivore of a southern kind, which ranged from Northern Italy, through France, as far north as Norfolk, before the lowering of the temperature during the glacial epoch, in company with several of the pleiocene species, such as the Cerius ardeus, Rhinoceros megarhinus, R. etruscus, Elephas meridionalis, and Trogontherium Cuvieri. The whole group of animals besides the above, associated with the Ursus Arvernensis in Britain, is as follows:
Mygale Moschata. The musk-shrew.
It is worthy of note that all the members of this fauna now alive are to be found in temperate regions, and there is every reason to believe that the extinct members also rejoiced in a temperate or comparatively warm climate. On the whole, we may predicate a southern range of the Ursus Arvernensis, just as in the case of two at least of the other British species we can predicate a northern origin. It defines with as much sharpness as can be hoped for in paleontology the pleiocene horizon of any strata in which it occurs, and particularly the stage immediately before the refrigeration of Central Europe had brought in the Arctic mammalia, and forced down southwards the pleiocene fauna of Britain, France, and Germany.
We must now pass on to the consideration of the cave-bear, . Ursus spelaus, the remains of which were among the first to be assigned to their true owners by the naturalists of the eighteenth century. The use of bones in medicine,* in the
* At the present day the Chinese are in the habit of using fossil-bones in medicine; and within the last few years the bone-caves of Borneo have been ransacked for the same purposes as the caves of the Hartz in the serenteenth and eighteenth centuries. To such a degree has this been carried, that up to the present time no European has been able to transmit home & collection of fossil mammalia from Borneo, because of the high price which the Chinese demand. The specimens described by Professor Owen from China, in the “Quarterly Geological Journal” for 1870, were bought by Mr. Swinhoe from Chinese who had collected them for physic. In the Chinese “Materia Medica ” they are described under the head of dragons teeth. Even human remains were commonly used in Britain in medicine during the seventeenth century. In the days of Sir Thomas Browne, “celestial mummice," or pulverised mummies, was commonly imported into Britain from Egypt; and it appears that even the tumuli round Abury were not safe from the incursions of eminent doctors.
In 1670 Dr. Robert Toope, a physician, then resident at Marlborough, in a letter to John Aubrey, gives a curious relation of the discovery, by labourers, of skeletons at this place (Abury), which, he says, had the name of Millfield. Dr. Toope terms the double circle a “temple," and describes it as “a large spherical foundation, whose diameter is forty yards ; within
sixteenth, seventeenth, and eighteenth centuries, caused the bone-caves of Saxony and Bohemia to be eagerly explored by the searchers after Album græcum, which in the old pharmacopeias did not merely mean elephant's tusk or hyæna's coprolite, but any fossil-bone whatsoever. And as among the remains obtained from the caves those of the cave-bear were very abundant, the similarity which they bore to the animal living in Germany led to the recognition of their true nature, and they were gradually withdrawn from the province of medicine into that of palæontology, under the name given to them by Dr. Goldfuss. During the latter part of the eighteenth and the first quarter of the nineteenth centuries the range of the cave-bear was gradually extended, by various discoverers of its remains, from Germany into France, and lastly, by the famous exploration of Kirkdale by Dr. Buckland, into Britain. It was discovered by the Rev. J. M'Enery, in Kent's Hole, and subsequently in no less than twenty out of the thirty-six British post-glacial caves, the contents of which I have tabulated in the “Quarterly Geological Journal,” 1869,
In Belgium, the limestone caverns around Liège yielded large quantities of its remains to Dr. Schmerling, the great rival of Dr. Buckland in cave-hunting. Recent investigations have shown that it crossed the Alps into Lombardy, and it has been met with also in Southern Russia. Its range in space may be said to extend from Yorkshire and Liège in the north, through Germany and France as far as the plains of Lombardy. It probably also found its way still further south in Italy, no geographical barrierintervening, although M.Cesselli's quotation of it from the gravel-beds of Rome has not as yet been verified. It has not yet been discovered in Northern Germany or Scandinavia, or in Northern Siberia, where the vast accumulation of fossil-bones have excited the curiosity of the most eminent naturalists, such as Pallas and Brandt. Its absence
this there is another orb whose sphere is fifteen yards in diameter ; round about this temple a most exact playne; and but little more than a foot under this superficies laid the bones soe close one by another that scul toucheth scul. I exposed two or three, and perceived their feet lay toward the temple; and I really believe the whole ground is full of dead bodies." He adds that the bones were large, but much decayed, though “the teeth were extreem and wonderfully white, hard, and sound;" upon which he notes: "no tobacco taken in those days.” Dr. Toope says: “I came the next day and dug for them (the bones), and stored myself with many bushels, of which I made a noble medicine, that relieved many of my distressed neighbours." Aubrey adds: “This was in 1678, and Dr. Toope was lately (1685) at the Golgotha again, to supply a defect of medicine he hath had from hence.”_"Crania Britannica, Ancient British," Kennet, vol. ii.