on these islands, at various heights above the sea, has shown that for a long time they have been rising gradually above the ocean; but, to add to our surprise, it is highly probable that the coralline islands, comprising all the non-volcanic islands, are gradually subsiding. The two phenomena go on in distinct parts of the ocean, no volcanic island existing within the areas of subsidence. The gradual change of level, which takes place on a large scale in parts of the ocean which are not subject to volcanic eruptions or earthquakes, is perhaps no less remarkable.

quent efforts? If the latter, then the changes to the volcanic islands of the Pacific Ocean. The which are now observed to accompany volcanic discovery of marine shells and fringes of dead coral eruption and earthquakes may be part of a series by which immense chains of mountains, like the Andes and Himalayas, have been produced. The inquiry in question has given rise to much discussion on the part of geologists. The view taken by those who hold the doctrine of primitive heat and gradual refrigeration has already been stated. Those who hold the contrary opinion derive much support from observations made on the Andes in South America, of which those of Mr. Darwin were not the least important. It has already been stated, that during the earthquake which occurred in Chili, in 1835, a large extent of land was raised several feet. There is a line, (says Mrs. Somerville,)* crossing Still more striking evidence of a rise Sweden from east to west in the parallel of 56° 3′ N. of land was observed by Mr. Darwin in the neigh-lat., along which the ground is perfectly stable, and borhood of Mendoza, on a ridge of mountains run- has been so for centuries. To the north of it for 1000 ning parallel with the chain of the Andes. At a miles, between Gottenburg and North Cape, the ground height of 7000 feet Mr. Darwin discovered a num- is rising, the maximum elevation, which takes place at ber of silicified trees rising from a bed of submarine North Cape, being at the rate of five feet in a century, lavas and sedimentary matter. These he supposes from whence it gradually diminishes to three inches to have once flourished by the shores of the Atlan- in a century at Stockholm. South of the line of static Ocean, now distant 700 miles. Subsequently bility, on the contrary, the land is sinking through they must have been buried beneath the ocean, part of Christiansad and Malmo; for the village of where they were covered not only with sedimentary Stapten, in Scanea, is now 380 feet nearer to the Balmatter, but, (as Mr. Darwin infers from their tic than it was in the time of Linnæus, by whom its present position,) by enormous streams of lava al- distance was measured eighty-seven years ago. The ternating with the aqueous deposits. Finally, these coast of Denmark on the Sound, the island of Saltholm, same trees, now in a siliceous state, were raised to opposite to Copenhagen, and that of Bornholm, are their present position, where they have been ex- The coast of Memel, on the Baltic, has actually risen rising, the latter at the rate of a foot in a century. posed to view by the detrition of the rocks in which a foot and four inches within the last thirty years, they were embedded. The rise of land which oc- while the coast of Pillau has sunk down an inch and curred during the earthquake of 1835, is supposed a half in the same period. The west coast of Denmark, by Mr. Darwin to be one in a series of elevations part of the Feroe island, and the west coast of Greenby which the whole west coast of South America land, are all being depressed below their former level. has been raised above the level of the sea. He In Greenland, the encroachment of the sea, considers earthquakes to act in a manner precisely analogous to volcanoes, in the one case melted matter being pumped into crevices occurring in the under surface of the crust, in the other the same matter being ejected. It is further suggested by him that the immediate cause of the interior convulsion is the giving way of the strata superincumbent on the sea of melted matter which, as we have already seen, he supposes to be spread out beneath the surface. The subsidence may be due to the tension produced by previous injections.

This theory of the gradual elevation of a chain of mountains is the only one, Mr. Darwin remarks, which will explain the fact that the axis of such chains has become solid under a pressure which the superior strata could not have exercised in their present inclined or vertical positions.

Closely connected with the subject of the elevation of mountain chains by means of earthquakes, is the inquiry whether volcanoes exercise a similar power, or produce elevation merely by the accumulation of the products which they eject.

The result of Von Buch's investigations into the geology of the Canary islands, was to convince him that some of the volcanic mountains in those islands owe part of their elevation to a distinct elevating force acting beneath the surface, and he was led to the conclusion that some of the crateriform depressions are not craters of eruption, but depressions due to the elevation of the surface from below. These craters were therefore called by him "craters of elevation." Much has been written for and against this doctrine, particularly with reference to appearances in the extinct volcanic region of Auvergne. The most striking facts in regard to the elevation of land are those, however, which relate

in consequence of the change of level, has submerged ancient buildings on the low rocky islands, and on the main land. The Greenlander never builds near the sea on that account, and the Moravian settlers have had to move inland the poles to which they moor their boats. It has been in progress for four centuries, and extends through 600 miles from Igalito Frith to Disco Bay.

It has also been shown that the land is rising in parts of Scotland.

VOLCANIC PRODUCTS.-Some examples of the different forms in which matter is brought to the surface by volcanic eruptions have already been given. The matter found in the neighborhood of volcanic mountains consists generally of one of three classes. It is either lava, scoriæ, or tufa. Lava is a dense homogeneous mass, which has not been thrown up into the air, but has flowed from the There are many crater in a uniform stream. varieties of lava-varieties in structure, form, and color. Some lavas are heavy and compact: others are light and porous. They are sometimes argillaceous, and often vitreous. The rock on which the castle of Lipari is built is composed of lava, which has partly passed into the vitreous texture. Lipari generally abounds in vitreous lavas. Obsidian and (probably) pitchstone are vitreous forms of lava, but do not often occur in the products of modern volcanoes.

Lava is generally of a dark color, but it is found of all colors, from almost white to nearly black. It is sometimes found of a beautiful red color.

The forms of lava are few. It is generally Tarpeian rock and of the Aventine and Celian hills amorphous that is, without any particular formare composed of this rock, which was used by the but occasionally modern lava, like basalt, assumes Romans for building purposes. a primitive outline.

Granular tuff is very different in external apVery curious changes take place in lavas which, pearance from stone tuff. It is of a blackish-brown like those surrounding the crater of Solfatara, are or yellowish-brown color, and of a much more exposed to the action of decomposing vapors. earthy character. It sometimes assumes a clayThey are frequently reduced to the state of powder, like aspect, and in this form is used for making and their color becomes quite white. The follow-bricks and earthenware. The Pincian, Quirinal, ing varieties are mentioned as occurring in Solfa- Viminal, and Esquiline hills, and the greater part tara. 1. A light lava, having the color of blue of the Celian and Aventine, are composed of a baked brick, of a coarse, earthy grain, and argil- peculiarly friable variety of granular tuff. laceous odor. 2. Of a cinereous color, containing iron pyrites. 3. An extremely white lava, almost reduced to powder, containing pyrites in layers. 4. A heavy lava, of a livid gray, abounding in pyritic crystals. 5. A lava white on the surface and reddish blue in the interior.

With the exception of Vesuvius, the greater part of the Phlegræan fields are composed of tufaceous rock. Naples is founded on tufa, and that rock is used as material for its buildings. The surrounding plain is tufa, and the hills to the north and west. The craters of the lakes Agnano and A peculiar kind of rock, known in Italy as Averno, parts of Solfatara, Monte Nuovo, the breccia, is sometimes found in the neighborhood of promontory of Misenum, and the island of Bocida, volcanoes. It consists of angular fragments of dif-are of this material. Herculaneum was destroyed ferent kinds of lava cemented together. It is often by a tufaceous torrent. Tufas are sometimes of various and very beautiful colors. The follow-formed almost entirely of pumice, and not unfreing kind is found in large isolated masses on the quently contain organic matter. The sand and island of Lipari; its principal substance is an ashes which are thrown out in such enormous earthy lava of a bluish gray, coarse grain, and quantities during volcanic eruptions, may be classed little hardness. It contains-1, lavas of a black under tufaceous rock. The fragments of which and gray color; 2, a vitreous lava of a beautiful they are composed frequently become bound tocolor, between green and blue, resembling pitch-gether after their fall.

stone; 3, numerous small pieces of a cinereous, All lavas contain iron, distributed in small compact pumice; 4, pieces of whitish, semi-trans- quantities throughout its mass. Occasionally this parent glass; 5, small pieces of a colored glass, resembling fictitious glass.

The number of minerals which are found in small quantities embedded in the lavas of Vesuvius is very numerous. Garnets occur frequently in some of its lavas.

iron appears to be expelled, and is found crystallized in vertical plates. The most remarkable example of this process is in Stromboli. When examined closely the plates are seen not to be plane surfaces, but to have a polygonal form. The faces of the polygons are of different sizes. The largest Scoriæ, so called from their analogy to cinders. exceed four inches in length, and three and a half are found in masses of small diameter, of a very in breadth. They have the brilliancy and polish rough exterior and porous structure, as if they had of the finest steel, and reflect the light like the been pervaded by gas. In other respects they re-most perfect mirror. In a similar manner, globules semble lava, and they are, no doubt, portions of heated lava broken off from the general mass, either before it issues from the crater, or whilst it is cooling.

Scoriæ sometimes assume a pear-like shape, when they obtain, in Italy, the name of bombes, or tears. At other times they have the appearance of twisted cables, trunks of trees, icicles, and other objects. They are found in Stromboli interspersed with beautiful colored crystals; some of the crystals being of a fine grass-green, others of an emerald color, and some a mixture of green and yellow.

of iron are sometimes found adhering to the external surface of lava. In the island of Ischia, and in other places, a ferruginous sand is found, in which the iron has a crystalline form. It occurs most abundantly by the sea-shore, and probably proceeds from the gradual wearing down of lava. Volcanoes sometimes eject masses of rock which do not appear to have undergone fusion—at least, recently. Thus Jorullo threw out fragments of granite; granular limestone is found in Somma.

Having mentioned the external forms of volcanic products, it remains to mention their internal structure.

When acted on by decomposing vapors, they undergo similar changes to lava; they lose their The minerals felspar and augite (the latter being color, become encrusted with sulphureous matter, probably identical in chemical composition with and are rendered so soft that they may be cut with hornblende) compose the greater part of the iga knife. Pumice is supposed to be the scoriæ of neous rocks of all ages. Modern lavas have been the glassy lava called obsidian. It occurs abun-classified as trachyte, greystone and basalt, accorddantly on the Lipari islands and in the Santorian archipelago.

ing as one or other of these two minerals predominates in them. In the trachytic lavas, felspar is in greatest quantity. In the basaltic, augite. Greystones are an intermediate class, which contain the two minerals in about equal proportions.

Tufa is a name given by the Italians to a rock, generally of an earthy texture, composed of an agglutination of scoria and other loose products of volcanoes. It occurs abundantly (the product, of Though volcanoes acquaint us with many new course, of extinct activity) in the neighborhood of combinations of minerals, they have not added to Rome, where two varieties-known as stone and the number of elementary substances. When regranular tuffs are found. Stone tuff is of a red-duced to their ultimate constituents, volcanic rocks dish-brown color, with orange streaks. It occurs are found to consist of the same matter as stratified in beds from one to six feet thick, intersected by rock. The following are the chemical analyses of vertical or sloping clefts. The summits of the felspar and augite :

six acres, in the waste of the nine-foot seam of 52.0 coal.

3.3

. 13.2
10.0

10.00

Of these minerals, therefore, silex constitutes more than half the weight. The analysis of the compound rocks shows that, in passing from the trachytic to the basaltic kind, the quantity of silica gradually diminishes. We give below the analysis of obsidian, (a trachytic lava,) of a greystone lava,

It is supposed to have been set fire to by some persons who had been distilling illicit whisky in it. Shortly after its discovery it rapidly extended 16.7 itself, and threatened the destruction of the entire 4.8 coal-field. A sum of £16,000 was laid out in surrounding the fire with a puddle-wall, to prevent its extending to other workings. The wall took five years in building, the workmen being frequently driven back, and obliged to recommence at a greater distance from the fire. It was, however, finally completed nineteen years ago. In the building of this wall the lives of nine men and three women were unfortunately lost at various times by the roof falling down and cutting off their retreat, and the fire overwhelming them before they could be excavated. One unfortunate girl was enclosed in this manner and not burnt, but roasted to death, so that, to use the expression of those who found her, when they took hold of her 2.25 arm to lift her it came off like the wing of a 2 60 roasted fowl. The fire having taken place near the crop of the coal it was surrounded by running the wall from the crop in a form resembling nearly a semicircle towards the dip, and then round again towards the crop, so that the line of the crop formed the diameter of the circle.

Basalt.

44.50

16.75

9.50

20'

2.

97.72

It will afford an interesting comparison, both with these analyses and with each other, if we now place side by side the analyses of granite and pumice :

Pumice.

Potash and Soda,.

30

1.7

Still, however, the wall required constant attention; as, if the fire once passed it, it would be a matter of great difficulty and expense again to surround it. In consequence it has cost the owner of the property (the Earl of Mansfield) about £200 a year in keeping it up, and in the payment of overlookers, there being always a danger of the fire 77.5 getting, by some accident, such as a fall of the . 17.5 roof, beyond the wall into the lower wastes, and burning the extensive coal field below. Various reports have from time to time been made by men of great authority in the coal trade, all of which have agreed in the utter impossibility of extinguishing this fire. It will, nevertheless, readily occur, that if the fire was thus, as it were, corked and bottled up to itself, it ought to have gone out from want of air. This, however, was not the case, for no part of the fire mine being deeper than twenty fathoms, and some of it running at no great distance below the surface, it obtained a sufficient supply of air thence, as well as through the leaksulky, and volcano-like existence-sometimes more ages in the puddle-wall, to maintain a smouldering, active, and sometimes less so, which could be traced by occasional falls of the surface, the last of which occurred about five months ago, laying bare the burning waste and discharging smoke and

99-7

It thus appears that, taking equal weights of granite and pumice, they give nearly the same chemical constituents. A striking resemblance is also perceived between the constitution of modern lavas generally and that of granite. Trachytic and basaltic lavas of ancient date are found, in some cases, to have penetrated granitic rocks, and in those cases must have originated below the granite. The date of these lavas, which are the earliest of which we have cognizance, is assigned as that of the appearance of the earliest tertiary rocks. But we must not extend these observations further, nor should we have extended them so far, had we not found that it was scarcely possible to give completeness to our sketch of this comprehensive and interesting theme within narrower limits.

BURNING WASTE OF CLACKMANNAN.

TO THE EDITOR OF THE TIMES.

steam.

fire mine, most of them partially filled. Some of There are about twenty-one old shafts into this them were sunk for the purpose of giving air to the workmen when building the puddle-wall, and some are old working shafts. There is also a drift running in a slanting direction from the crop, which was a clear passage for about sixty yards, and was then partially stopped by falls, of the roof, but through which there was sufficient opening for air to pass into the mine. This drift served for an upSIR-The public will, I feel sure, be deeply in-cast. Near to the wall was a shaft, at the opposite terested in an experiment on a gigantic scale which side of the burning waste, which, in this experihas just been brought to a satisfactory conclusion ment, served as a downcast into the waste. under the superintendence of Mr. Goldsworthy Lord Mansfield's attention was called by the Gurney. The object of the experiment was to ex-members of the committee of the House of Lords, tinguish a fire in the South Sauchie colliery, near who sat in 1848 to consider the best means of preAlloa, about seven miles from Stirling, which has venting accidents in coal-mines, to the evidence raged for about thirty years over an area of twenty-then before them of the fact of a burning coal-mino

at the Astley Collieries, Lancastershire, having the space is filled, both of which principles were been extinguished by the singular process of pour- recognized and acted on during the process of cooling in choke-damp, suggested and carried out by ing, a process which Mr. Gurney considered of Mr. Gurney, a report of which, in a letter dated great importance. In conversation with him on the 30th of April, 1849, appeared in The Times of this point, previous to his leaving town, I made a the day-a fact so difficult to believe, and appar- suggestion which he was pleased to consider imently impossible, that it was not generally credited, portant, and at his request I accompanied him to except by men of science. Lord Mansfield com- the field of action, and was present during the conmunicated with Mr. Gurney, who inspected the flict with our underground antagonist. fire mine immediately after the rising of the committee of the lords, accompanied by Mr. Mather, the honorary secretary of the South Shields commission, Mr. Darlington, the proprietor of the Astley Colliery, and Mr. Jamieson, sheriff clerk of Clackmannan. After this inspection Mr. Gurney reported to Lord Mansfield that, notwithstanding the immense extent of the burning waste, he thought it possible to extinguish the fire; and, ex-in diameter and about nine feet long. The cylintraordinary as it may appear, this object has been effectually accomplished by a simple and inexpensive process.