BOLCA, MOUNT. About eighteen or twenty miles north-east of the city of Verona, there is a small village called Bolca, from which a mount, or hill, re ceives the same appellation. The village itself is not of sufficient consequence to merit a particular descrip tion, but it is otherwise with the hill, for in its sub stance are contained some of the most remarkable na tural productions Which the world affords.
Around Mount Bolca, and throughout the territo ry of Verona, unequivocal volcanic remains demon strate the prevalence of subterraneous eruptions, and also that the whole must have once been covered by the sea. Numerous petrifactions of plants, shells, and marine animals, are dispersed in the earth, but fre-, quently in such an arrangement, that beds in one dis trict are confined to certain species unmixed with others, while the same peculiarity is observed in dis tricts more remote. In the mountains, whereof Bolca is one, there have been found 27 genera of Testacea, hitherto unknown ; and less than 200 species of petrified shells have been dug from the tufa, marbles, and basalts, of which the neighbouring territory is com posed. By a wonderful accumulation, shells, whose animals inhabited different seas and different climates, are collected together in the same heap, along with those which never retreat to water. There are also Many petrifactions of zoophytes, consisting of the articulations of asteriz, clusters of corals, and madrc pores ; and in this unaccountable aggregate, the parts of terrestrial quadrupeds, of birds, and of insects, arc not wanting. The bones of huge elephants, stags, and bears, and likewise those of an intermediate tribe, the phocx, have be'n discovered. Basaltic columns of various kinds are seen on Mount Bolca, and in the neighbourhood, differing not only in structure, but in the proportions of their elementary parts. Their figure is hexagonal, pentagonal, quadrangular, and even triangular ; and their position is generally per pendicular to the horizon ; but at San Giovanni d'I larione they exhibit a degree of obliquity, as if some disturbing cause had altered their position. Burnt earth, scorie, lava, and other volcanic productions, are scattered about the Purga di Bolca ; and the hill itself, barren of vegetation, is covered with earth intermixed with animal and vegetable remains. These circum stances, added to the natural phenomena which will come under our consideration, plainly shew,' that the tract environing Mount Bolca has been subject to. volcanic eruptions, and that the sea has covered it at some very remote period. At present, the nearest shore is fully fifty miles distant from its base.
Part of what passes by the general name of Mount Bolca, is situated at a short distance from the real hill, and called Lastrara ; so that, according to the strictest topography, they should be separated : but no such division being spoken of when those who precede us treat of the productions of the place, we shall follow their example, in considering Bolca and Lastrara as synonymous.
All the fossils of the Veronese territory are siderable when compared with innumerable petrified fishes found in Bolca, where it would seem as if the whole seas and rivers of the globe had concurred in depositing their contents. Those of Europe, Asia, Africa, and America, are huddled together in one confused heap : the fishes of the torrid zone are mix ed with those of temperate climates ; those of fresh water rivers with those of the most extensive seas ; and all differing in habits, structure, and properties. Large masses of stone, detached and unconnected with the ordinary substance of Mount Bolca, lie im bedded in the side of the hill, 1000 feet above the level of the sea. Quarries penetrating into these,
have exposed the fossil fish to view. The stone con taining them is calcareous, of a schistose structure, and susceptible of being split into flags, or lamina', of various thickness and dimensions ; and it has been denominated by mineralogists a marl or marley schist. It is of a whitish, yellowish colour, or of a bluish grey, and some of it is quite black. Its hardness, though of different degrees, is such as commonly to yield to the knife, but not to the nail ; and it has one characte ristic peculiarity, which consists in emitting a peculiar fetid odour on being struck, or rubbed, compared to that of swine-stone. This odour, the Abbe Fortis, ' in treating of petrified shells found not far from Boles, supposes to proceed from animal putrefaction. On splitting the flags asunder, the remains of petrified fishes appear of a dark brown colour, and are constt quently very conspicuous on the light ground of the stone. They lie flat between the lamina; their contour and component parts being little, if at all, distorted from their natural shape and dimensions ; but some times there is an enlargement or defect, arising either from the changes undergone in passing from an animal to a fossil state, or by the stone apparently.having been affected by motion after they were inclosed within it. Their whole form is completely defined, and the harder parts, such as the head, fins, spine, and other bones, are still more evident. The dark brown sub stance composing the fish remains quite distinct, and projects from the lamina of the stone, in proportion to the size of each part in its natural state, and it may be separated from the stone. It is hard, brittle, and rather glossy, excepting some of the larger bones, • such as the joints of the vertebrx, which, though presenting the same external appearance, exhibit ca vities filled with beautiful crystals. The different colour of the slate, or. flag, inclosing the fishes, has been ascribed by naturalists to the chemical effects of their bodies on the stone, which is not improbable, on reflecting that it could not be originally in an in durated state. Fossil fish are found in various parts of the world, and high above the present level of the sea, but no where in the same abundance as in the quarries of Mount Bolca ; and the fishes of this hill. are further distinguished from the impressions usually seen in argillaceous schistus, as well as from the pc trifactions of shells found in limestone strata. In the latter nothing more than the simple impression of remains, and the external shape of the shell is alone preserved, whereas, in the productions of Bol es, the form and size of the animals are not only ad mirably exhibited, but there even seems to be the re sidue of animal matter, in that substance which we lave said may be detached from the stone. Inspec tion determines it to be of a different nature from. that of the inclosing stone, and, so far as could be judged without analysis, those naturalists who have. bestowed most attention on the subject, conclude it to be animal remains ; and that it is in a condition similar to the flesh of mummies ; from which cir cumstance Volta denominates the state of these fishes natural embalming. _ Most of the fishes of Bolca are, such as now inha bit the European seas, but there arc some species peculiar to the rivers of India -and America exclu sively, while there are many belonging to the fresh water streams of our own and neighbouring coun tries. It, is asserted by .observers, that petrified American fishes are found in no other part of Eu rope, notwithstanding there are numerous impres sions of European ones in France, Switzerland, Ger-, many, Britain, and elsewhere.