after gold had been discovered in these states, the inhabitants were content with searching for gold in the beds of the brooks and rivers after heavy rains. One of the proprietors of a gold stream, having noticed that it never yielded gold above a certain point, where a small brook entered into it, was induced to trace the brook to its source, and discovered in the adjacent rocks, veins of quartz which were found to contain pieces of native gold, and were subsequently worked as mines. It is highly probable that in Africa, the sands in certain parts of rivers become auriferous, by the depositions from rivulets that flow into the main stream.

Mr. Hennah, of Plymouth, has in his collection several pieces of native gold, varying from the size of a bean to that of a hazel-nut; they were found in stream works near St. Austel: he has also a specimen of stream tin, eight or nine inches in length, and five or six in breadth, which was evidently, once, part of a vein. In the same stream work they could distinguish at different depths, the different veins from which the ore had been washed out. The pebbles of tin ore, have, in some situations, been washed into the sea, and afterwards covered by beds of clay or gravel. In Mount's Bay, south of the town of Penzance, there was formerly a bed of stream tin worked under the sea. The stream tin covers the killas or slate rock of the country, and is covered by a bed of clay: a perpendicular shaft or tunnel was sunk through the clay, and the bed of stream tin was worked like a bed of coal, the clay forming the roof. See Plate VII. fig. 8. The workings were continued under the sea, but were at length inundated and discontinued.

The bed with pebbles of tinstone, is seen covering the beds of slate; upon this is a thick bed of water tight clay, over which the tides roll. An iron cylinder was sunk through the clay as a shaft to the tin stone, which was worked like a bed of coal and drawn up the cylinder.

The following is a summary account of the rocks in which the different metallic ores are generally found:

Platina and the recently discovered metals called palladium, rhodium, osmium and iridium, have been found only in the sands of rivers.*

Gold and silver are found in primary and transition rocks, in porphyry and sienite, and in the lowest sandstone. Gold has been occasionally discovered in coal, and very abundantly in the sands of rivers, and sometimes in volcanic rocks.

Mercury is found in slate, in limestone, and in coal strata.

Copper, in primary and transition rocks, in porphyry, sienite, and occasionally in sandstone, in coal strata, and alluvial ground. Mass

Boussingault discovered platina along with oxide of iron and gold in Sienite, near Santa Rosa, in the province of Antioquia.-Ann. de Chim. et de Phys. t. 32. p. 209.-B. S.

es of native copper of many thousand pounds weight, are said to be found on the surface, in the interior of North America.

Iron in every kind of rock.

Tin, in granite, gneiss, mica-slate, and slate.

Lead and zinc, in primary and transition rocks, except trap and serpentine; in porphyry and sienite; in the lowest sandstone, and occasionally in coal strata.

Antimony in primary and transition mountains, except trap and serpentine; it is also found in porphyry and sienite.

Nickel, bismuth, cobalt, in primary mountains, except limestone, trap, and serpentine. Cobalt and nickel also occur in transition. mountains, and in sandstone.

Arsenic, in primary and transition mountains, and in porphyry. Manganese, in primary and transition mountains, and occasionally in the lower stratified rocks.

Molybdena and tungsten, uranium, and titanium, in granite, gneiss, mica-slate, and slate. The latter metals, with chromium, columbium, cerium, and tellurium, are very rare in nature, and can only be reduced to the metallic state with great difficulty.

CHAPTER XX.

ON SUBTERRANEAN RIVERS AND CURRENTS, AND ON CAVERNS.

Occurrence of Subterranean Currents and Rivers in various Parts of the World.The Principal Agents in the Formation of Caverns.-Remarkable Cavern and Cascade in the Speedwell Mine, Derbyshire.-Subterranean Currents and Caverns generally in Calcareous Mountains.-The reason explained.—Subterranean Currents connected with the Surface Water, deposit Animal and Vegetable Remains between ancient Strata, proved by Facts.-Caverns with bones of extinct Species of Animals in Germany and France, intermixed with Human Bones, and Implements of Industry.-Bones introduced into Caverns by Subterranean Currents and other causes, and at different Epochs.-Cavern at Kirkdale, in Yorkshire.-Bones found in the Clefts and Fissures of Rocks forming Osseous Breccia in various Parts of Europe, and in New Holland.-Epochs of their Deposition supposed to be different in distant Parts of the Globe.

BESIDE the fissures and spaces filled with metallic matter, that occur in the older rocks, as described in the preceding chapter, there are empty spaces or caverns, that sometimes extend far into the interior of mountains, and sometimes descend to considerable depths. Almost all large caverns occur in limestone rocks, chiefly of the transition and the secondary class. Caverns, in some instances, may have been formed by the upheaving or subsiding of rocks; but they have, most frequently, been excavated by subterranean currents of water, which have enlarged original fissures, or carried away the beds of soft clay or loose sand that were interposed between hard strata. Many large caverns have streams of water constantly running through them; and, after heavy rains, they are often gorged with water, which issues with violence from their mouths. This is the case with the great Peak Cavern, near Castleton, in Derbyshire.

The action of subterranean currents of water, has scarcely been attended to by geologists; but were it better understood, it might probably afford a satisfactory explanation of several facts in geology that have been regarded as anomalous, particularly that of the occurrence of bones in caverns which have no opening to the surface. In the third edition of this work, I stated some instances of these currents in mountain limestone.

The mountain or transition limestone of Craven, in Yorkshire, forms, in many parts, a nearly flat elevated surface of table land, covered with vegetation, but intersected by numerous fissures or chasms of vast length and depth, varying from a few inches to a foot or more in width. Many of these fissures widen as they descend; and at the bottom, streams of water may be, frequently, heard running. During snow, it is not uncommon for sheep to be lost in these chasms, and the whole surface is extremely dangerous, to traverse in the dark. Limestone plains, intersected by such fissures, may be regarded as natural traps for herbivorous animals, into which, when

chased by beasts of prey, they may fall in whole droves. Their bones may either stick fast in the fissures, and be afterwards inclosed in calcareous stalactites, or they may be carried by subterranean. currents into caverns which have no communication with the surface. Such was the cavern at the Bull's Eye mine, near Worksworth, in Derbyshire, which was opened by mining operations in the year 1663, and contained the entire skeleton of an elephant.

There is a considerable river, called the Pinka, in the cavern at Adlesberg, in Carniola, which forms a subterranean lake, where it appears to be lost; but it emerges again on the north side, and takes the name of the Renz. This cavern is one of the largest in Europe; it extends for several leagues into a calcareous mountain, situated between Laybach and Trieste, and contains the bones of bears and other animals, in the mud that forms the floor of the cavern, or rather series of caverns, that are connected by passages with each other.

There are numerous caverns and grottoes in the vicinity of Adlesberg, and the surface of the country is, in various parts, broken by depressions from the subsidence of the roofs of these caverns. There are doubtless, in all these caverns, subterranean rivulets, which are continually in action, and are undermining and wearing down the rocks that support the strata above them. In Derbyshire, and the district called Craven, in Yorkshire, beside the subterranean rivulets before mentioned, there are currents of water incessantly in action, which are discovered only by mining operations.

The Speedwell mine, near Castleton, in Derbyshire, is a subterranean tunnel and canal, nearly half a mile in length, penetrating into the centre of a mountain, composed of metalliferous limestone: the descent to the canal is by a flight of steps, about forty yards in depth. The mountain is intersected by numerous metallic veins, and the proprietors of the mine intended to carry the tunnel and canal through the whole extent, in order to discover the veins, and have ready access to work them, to bring out the ore. It was necessary to excavate the stone by blasting, and before every explosion the miners retired for safety to a considerable distance in the tunnel. When they had proceeded in this manner about eight hundred yards, they were greatly alarmed after a blast, to hear the tremendous roaring of a torrent, and fled towards the entrance of the tunnel. A miner, who was working there at the time, informed the author, that he thought there was no chance of their escaping immediate destruction; however, when they had retreated a considerable distance, they perceived the rushing sound to grow less alarming; they then halted awhile, and took courage to return, when they discovered that the last blast had made an opening into a spacious cavern, and that a torrent of water was falling from a considerable height into a vast chasm on one side of it. The loud roaring of the water was greatly increased by the echoes of the cavern; for in the roof of this cav

ern there is a wide opening into an upper cavern, the top of which is not visible from below, even with the illumination of fireworks, which those who show the mine generally take with them.

By the ceaseless action of such internal currents of water, falling into original fissures, or descending through soft strata in mountains of compact limestone, it is easy to conceive that caverns of great extent may be excavated. A very few years since, a miner, in driving an adit or passage into the heart of the well-known rock called Matlock High Tor, discovered a large cavern and a lake in the middle of the mountain. Many of the coves or caves in Craven, in Yorkshire, were originally caverns, the roofs of which have fallen in; they have streams of water rushing into them, forming subterranean cascades. The cavern called Weather Coat Cove, and the rocks at Gordale Scar, offer illustrations of the effects of subterranean currents. Where springs of water of considerable magnitude rise at once to the surface, it is obvious that they are not the result of slow percolation through porous strata, but that they are the outlets of internal streams or rivers. The river Air rises at the foot of a perpendicular limestone rock, called Malham Cove, in Craven; it is a broad, powerful, and permanent stream, before it receives any tributary rivulets from the adjacent valleys. It is generally believed that the subterranean stream which gives rise to the river Air, is connected by internal passages with Malham Tarn, a mountain lake, situated at a considerable distance. Perhaps the spring at Holywell, in Flintshire, may be cited as offering a similar proof of underground rivulets.

The reason why subterranean streams of water, and extensive caverns, should occur chiefly in districts where compact transition or mountain limestone is the prevailing rock, will admit of an easy explanation. Slate rocks are almost always intersected by perpendicular fissures, which carry off the water, and prevent its accumulating in large streams; and the secondary strata in England are generally too soft, or too much broken, to form the roofs of extensive caverns, or the beds of subterranean rivers. In the vicinity of the Alps, where the secondary limestones are extremely hard and compact; they contain caverns, and afford a passage for subterranean currents. A considerable cavern has, however, been recently discovered in mica-slate and common slate, in the Isle of Thermia, one of the Cyclades, at the height of 1400 feet above the level of the sea. M. Virlet, who visited the cavern, attributes the excavation to subterranean streams of water, as there is a considerable deposition of mud and bluish clay at the bottom of it.-Séance du Fév., 1832, de la Société Géologique de France.

It is admitted by M. Desnoyers, in the report from which this account is extracted, that the existence of such a cavern in rocks of mica-slate and slate, is a new fact in geology. There are several thermal springs in the island, which indicate the action of subterra