the older rock-systems below, or to the superficial accumulations above. Compare the price of an estate in the Cleveland district of Yorkshire in 1853 with its value in 1874; estimate the worth of a poor moorland tract in Linlithgowshire in 1856 with its value (for oil-shales) at the present moment; or the importance of a farm on the Greensand (with phosphate nodules) at these respective dates,—and no further argument will be necessary to establish the advantage of having in every instance of sale or purchase a thorough investigation of the geological features and mineral resources of estates.

To obviate the risk of parting with unknown wealth for no adequate equivalent, the minerals of an estate are sometimes reserved, and the mere surface or solum disposed of. This practice, while it guards the seller, not unfrequently becomes a source of extreme annoyance to the purchaser or his successors. It is true they have their surface damages for any roads or excavations that may be made in quest of the minerals; but there is none for loss of amenity by smoking iron-heaps, brick-clamps, waste mounds, and other unsightly adjuncts, while very often a rough and troublesome population is brought to the vicinity, and poor-rates increased by their improvidence as well as by the dangers of their occupation. It is true, no one can tell when certain minerals are to rise in value, or when worthless substances are to be utilised; and it seems hard that through such utilisation estates sold twenty years ago may now be worth three times the money then paid; but in face of such contingencies, it seems better, on the whole, that sales and purchases of estates should be entire and absolute the sellers taking every precaution to have the highest price for their conjoint agricultural and mineral capabilities. Some mineral substances may fall into desuetude, and others may acquire new and unexpected values; but, generally speaking, in a mechanical and manufacturing country like Britain, the tendency will be towards a greater consumption, and consequently towards increased demand and higher prices. Taking this view, the seller of a mineral estate is justified in seeking a higher price, and the purchaser, on the other hand, equally safe in offering it.

The same remarks hold good with respect to mineral leases. A farm may be let for nineteen years, as is usual in Scotland, and yet at the end of the lease, if proper precautions have been taken as to cropping and rotation, the soil may be richer and more valuable; but at the end of a mineral lease the materials removed are gone, and for ever. No landed proprietor, therefore, who studies his own interest or the in

terest of his successors, should, in the increasing value of mineral produce in Britain, grant long leases; and in such leases as he grants, should always stipulate for a lordship proportionate to the market price of the substances disposed of. Millionaire iron and coal masters would have been fewer in number had landowners been sufficiently provident in the leasing of their mines and minerals.

In the preceding remarks we have restricted ourselves almost exclusively to the sale and purchase of estates in the British Islands, but the same precautions are equally necessary in the selection and purchase of land in our colonial possessions. It is not always fertile soil and surface amenity which should determine the settler's choice. The finest soil and situation, unless for town-lots, will never bring more than an average agricultural return; while some poor and forbidding tract may contain within it inexhaustible stores of minerals and metals, which will continue to rise in demand and value the more the population increases and settles down to commercial enterprise and industrial activity. A little geological knowledge, and a few months spent in prospecting along the sea-cliffs, up the river-banks, and over the rocky surfaces wherever these may be exposed, will always repay the colonial settler, even should he have to wait several years for the development of the mineral resources of the tract he has chosen. Nor does it require much geological skill to detect the presence of the more important minerals and metals. Coals and coaly shales soon reveal themselves in any section; ironstones show themselves by their oxidised or rusty surfaces, and are usually accompanied by springs or trickles of water leaving an ochrey deposit; limestones weather into whitish or whitish-brown surfaces, and are frequently accompanied by petrifying springs; copper ores show various tarnishes of green, reddish, or pavonine tints, and are accompanied by trickles having a strong styptic and coppery taste; lead ore or galena, by its leaden-grey colour and cubical cleavage; antimony ore, by its lighter-grey colour and long radiating crystals; while the metallic ores in general may be readily detected from stony minerals by their greater weight and metallic lustre in the fresh-made fracture.

It should be obvious, from what has been said in the preceding paragraphs, that every landed estate has a twofold value-one depending on its superficial qualities and their susceptibility of improvement, proximity to roads, public burdens, and access to markets; and another arising from its

mineral resources, their nature and abundance, facilities of winning them, and amount and continuance of demand, existing and prospective. In selling or in purchasing landed property, these values should be respectively taken into account, and no reasonable trouble or expense withheld in approximating their amount by careful and competent surveys. In such surveys some knowledge of geology is indispensable, whether relating to the soils and subsoils above, or to the minerals and metals below. Nor, when these respective values have been ascertained, should it ever be forgotten that they differ in this important essential-namely, that while the superficial value is ever increasing by judicious treatment—draining, trenching, planting, &c.—the mineral value, by working, is ever diminishing, and in the end may be wholly extinguished. Than this, no fact can be more obvious, and yet it is too often disregarded in arranging for the interests of heirs and successors.

Works which may be consulted.

Brown's Book of the Landed Estate;' Lintern's 'Mineral Surveying and Valuing;' Hudson's Land Valuer's Assistant;' Donaldson 'On Landed Property.'

V.

GEOLOGY AND ARCHITECTURE.

PART I.-BUILDING AND DECORATIVE STONES.

THE relations of Geology to Architecture are at once intimate and important. All our building-stones, stones for internal decoration and sculpture, mortars and cements, concrete and artificial blocks, are obtained directly or indirectly from the crust of the earth. It is not merely shelter and defence that man seeks from his structures; he has æsthetic tastes, and hence beauty of colour and texture, and capability of being fashioned and combined for the production of general effect, become important properties in the architectural materials with which he has to deal. The stone suitable for the massive fortress may be unfitted for the lighter mansion, and the material adapted for the country villa might be unsightly in the city street; while tints in keeping with the plain frontage of a warehouse might ill accord with the ornamental fretwork of a cathedral church. Besides, the stone that will endure under a dry and equable climate may waste and weather away under a humid one; while that which will retain its colour and freshness in the air of the country may get dingy and corroded under the carbonated atmosphere of a manufacturing town. Nor is it alone colour and texture and general durability that have to be studied; the modes of bedding and tooling and dressing suited to different stones are also important elements for consideration, as what might tone down the colour in one, and mask the rough texture of another, might altogether be a disfigurement to a third. Again, toughness or resistance to strain and pressure is paramount in stones for lofty and heavy structures, the hardest texture not being always that which will endure the highest crushing power. Another consideration is the structure or natural masonry of the rock in the earth's crust -whether it be thick-bedded, flaggy or slaty, tabular, jointed, or columnar-as on this structure depends its capability of being raised in blocks of sufficient size for any special requirement.

These and many kindred considerations have to be taken into account by the architect and builder; but so far as our present purpose is concerned, the lithology of the materials which they have most frequently to deal with may be arranged under the following heads: 1. Building - Stones; 2. Stones for Decoration and Sculpture; 3. Limes, Mortars, and Cements; and 4. Concretes and Artificial Stones.

I. BUILDING-STONES.

In building-stones for edifices (other than those of docks, piers, and breakwaters, to be noticed under Civil Engineering, Chap. VII.), the main requisites are beauty of colour and texture, durability, and facility of being dressed and tooled. These qualities vary very much in different rocks, some freestones being of beautiful colour and texture, and very readily quarried and tooled, but far from durable; some granites and porphyries extremely durable and of pleasing tints and lustre, but expensive in dressing; and others, like some grey grits and greenstones, both durable and easily tooled, but very sombre and unsightly in colour. In noticing these and other varieties, we shall dwell mainly on the building-stones of our own islands, only touching, by way of illustration, on those of other countries, whether modern or ancient. And first of the Granites, Porphyries, Greenstones, Felstones, Basalts, and other kindred rocks of igneous origin and of pyro-crystalline or pyro-plastic texture.

The Granites and Porphyries.

This

The granites, which were early used, especially in Egypt, for monoliths and gigantic sculptures, form a numerous family, differing widely in colour, texture, and durability. In our own country they have come largely into use within the present century, both for structural and decorative purposes. is chiefly owing to their durability and susceptibility of fine polish, but partly also to the invention of mechanical appliances by which their dressing can be facilitated. They differ considerably in their mineral composition, colour, texture, and facility of being raised in large blocks, but are all old igneous rocks, amorphous or tabular in structure, crystalline in texture, and occur chiefly associated with our most ancient hill-ranges, though in some regions they burst through strata as recent as the Jurassic and Cretaceous. Certain stratiform granites are regarded by some geologists as of metamorphic origin, but