Limestone, or Statuary Marble, by having a less decidedly crystalline texture. Where this rock lies directly upon slate, it contains few organic remains; but where Red Sandstone is interposed between it and the Slate Rocks, or in proportion as it is distant from the Primary and Slate Rocks, the relics of organization become more frequent. It then abounds in remains of corals and zoophites, (sponges) which now are not known to exist. It is often traversed by veins of calcareous spar, and presents a great variety of colours. It is abundant in Devonshire, South Wales, Derbyshire, and Yorkshire; and is commonly known by the name of Mountain Limestone. At Plymouth this rock is seen immediately incumbent upon slate, in a quarry between the dock and the town. Its colours are red and gray, streaked with white crystalline veins. It is also seen to great perfection in the Breakwater quarries at Orestone.

MAT. Of this I suppose the Break water at Plymouth is constructed.

MRS. L.-It is so. It is, I believe, a mile in length, and at the base 100 yards wide. Many of the masses of marble used in this extraordinary work are of more than ten tons weight: they are merely thrown upon each other without cement, and gradually fixed together by the weeds that grow about them; in which state they have resisted the most violent storms of that tempestu

ous sea.

ANNE. You said, I think, that these Transition or Secondary Limestones do not exactly resemble the Primary in appearance.

MRS. L.-For the most part they have a more earthy and less brilliant appearance; but it is not always possible to distinguish them without knowing where they come from. I will presently show you several specimens. Limestone Strata are very remarkable for the inflections and curvatures, referred by Dr. Hutton to their having been in a soft state at the time they were disturbed from their horizontal position. There are some very curious

instances of these curvatures noticed by Saussure, one in particular on the road from Geneva to Chamouny, where the stream of Naüt D'Arpenay forms a cascade by falling over a perpendicular surface of Limestone Rock; the Strata are bent into regular arches, with the concavity to the left; while in another neighbouring mountain they turn to the right; so that a vertical section of the two would present the figure of S. The top of Benlumers in Perthshire, and the coast of Berwick, with many other districts in Scotland, present instances of these singular contortions.

MAT.-I suppose we should have no difficulty in finding districts of Limestone in our short country excursions.

MRS. L.-They are very abundant in this country, and I believe every where else. "The aspect of a country of mountain Limestone is peculiar, and generally extremely picturesque. The hills which, in this country at least, are not very lofty, abound in precipices, caverns and chasms, and when upon the coast, form small promontories, and jut out in low but grotesque pillars. The even surfaces are covered with a stinted turf, but the rifts and cracks contain often a soft rich soil in which stately timber-trees flourish. The chasms of Limestone Rocks are often filled with a fine Clay, which has perhaps sometimes been derived from the decomposition of shaly strata, or sometimes deposited from other causes in the fissures; and the singularities of aspect, and much of the beauty of this rock, is referable to these peculiarities. Thus, upon the banks of the Wye, large and luxuriant trees grace the abrupt precipices, and jut forth from what appears a solid rock. Their roots are firmly attached in some crevice filled with a favourable soil. Sometimes rivers force their way through the chasms; at other times they are empty, and the roofs ornamented by Nature's hand with stalactitical concretions of white and glistening spar, which seem like the fretted sculpture of Gothic architecture."

"The delightful views of Matlock and its vicinity, and the caves of Castletin are admirably illustrative of the scenery of Mountain Limestone. Pontheath Vaughn in Glamorganshire, is full of its beauties; and the Panorama of Swansea Bay, seen from the Mirables Point, furnishes a pleasing, characteristic, and perhaps unrivalled prospect of these rocks. The banks of the Avon too, in the vicinity of Chepstow, are of Mountain Limestone. The rock is there impregnated with Bitumen, and hence exhales a peculiar and fetid odour when submitted to the blows of the axe or hammer. This is by no means uncommonly the case where the Limestone Rock, as in the present instances, is in the vicinity of Coal.

ANNE.-Is this Stone of any other use than for building?

MRS. L.-It is an excellent material for that purpose, as we have seen, and many of its varieties are sufficiently hard to receive a good polish, and are thus employed for ornamental purposes, being cut into vases, chimneypieces, and the like. "Where they abound in corals, and other organic remains, these frequently add to their beauty. In those rocks which contain no organic remains, and even in many in which they exist, the colour is uniform throughout. In these cases, scarcely any tint is found, but the innumerable varieties of grey; at one extremity of which may be placed pure white, and black is sometimes at the other. Ochre yellow tints are occasionally to be observed, but varieties of red are far less common. Where organic remains are imbedded, the colours of these bodies and those of the base are sometimes different; the former being white or light grey, while the latter are dark. In other instances a much greater variety of hue prevails-different tints of -yellow, red, grey, white, and black, being sometimes intermixed in various modes." The black variety, known by the name of Black Marble, or Lucullite, in consequence of the admiration bestowed upon it by Lucius B b

VOL. VII.

Lucullus, has long been admired, and is often tas fully manufactured and ornamented by etching upon its surface. It is found in Derbyshire, Sutherland, and Galloway.

MAT. Of what is Limestone composed?

MRS. L.-The ingredients vary-but the essential parts are Carbon and Lime. All these Limestones are convertible into a more or less Quick Lime by the operation of a red heat, and are thus valuable as affording manures, and for other purposes. This is Lime as we see it laid on the fields, made into mortar, and for other

uses.

There is a sort of Limestone distinguished from the above, by the large quantity of Magnesia it contains, whence it is called the Magnesian Limestone. "It prevails considerably in England-is distinguished from the common Limestone in external character, by having generally a granular, sandy structure, a glimmering lustre, and a yellow colour. In the course of the range, from Nottingham northward, its surface in many places is covered by a poor herbage, uncommon to Limestone, and attributable to the Magnesia it contains, which is known to be unfavourable to vegetation. Its general colour is buff, but it also occurs white, of various shades of yellow; also of fawn and salmon colour, occasionally of a brown or reddish hue. It is employed as a building stone, and has a pleasing tint; at Broadworth it is worked into cisterns, and at Langwith, in Derbyshire, into flooring and staircases. It is rarely uniform enough in its grain, or of sufficient hardness to deserve the name of Marble."

ANNE. What is Magnesia?

MRS. L.-It is an earth, generally found mixed with other substances-in itself it is soft, of a greyish white, and adheres slightly to the tongue. I will now show you a few specimens of Limestone, of which the appearances are very numerous. Fig. 1, is the common Mountain Limestone-if mixed with acid, it effervesces.