REQUISITES FOR GOOD BUILDING STONE.
The qualities which are most important in stone used for construction are cheapness, durability, strength, and beauty. The relative importance of these different qualities varies greatly with the nature of the structure and with the personal opinion of the engineer or architect.
The factor which usually determines the value of a stone for structural purposes is its cheapness. The items which contribute to the cheapness of a stone are abundance, proximity of quarries to place of use, facility of transportation, and the ease with which the stone is quarried and worked.
The wide distribution and the great variety of good building stone in this country are such that suitable stone should everywhere be cheap. That such is not the case is probably due either to a lack of the development of home resources or to a lack of confidence in home products. The several State and Government geological surveys have recently done much to increase our knowledge of the building stones of this country.
"The lack of confidence in home resources has very frequently caused stones of demonstrated good quality to be carried far and wide, and frequently to be laid down upon the outcropping ledges of material in every way their equal. The first stone house erected in San Francisco, for example, was built of stone brought from China; and even in 1880 the granites mostly employed there were brought from New England or from Scotland. Yet there are no stones in our country more to be recommended than the California granites. Some of the prominent public and private buildings in Cincinnati are constructed of stone that was carried by water and railway a distance of about 1500 miles. Within 150 miles of Cin cinnati, in the sub-carboniferous limestone district of Kentucky, there are very extensive deposits of dolomitic limestone that afford a beautiful building stone, which can be quarried at no more expense than that of the granite of Maine. Moreover, this dolomite is easily carved, and requires not more than one third the labor to give it a surface that is needed by granite. Experience has shown that the endurance of this stone under the influence of weather is very great; yet because it has lacked authoritative indorsement there has been little market for it, and lack of confidence in it has led to the trans portation halfway across the continent of a stone little,. if any, superior to it." Development of local resources follows in the wake of good information concerning them, for the lack of confidence in home products can not be attributed to prejudice.
The facility with which a stone may be quarried and worked is an element affecting cheapness. To be cheaply worked, a stone must not only be as soft as durability will allow, but it should have no flaws, knots, or hard crystals.
Next in importance after cheapness is durability.
Rock is supposed to be the type of all that is unchangeable and lasting; but the truth is that, unless a stone is suited to the con ditions in which it is placed, there are few substances more liable to decay and utter failure. The durability of stone is a subject upon which there is very little reliable knowledge. The question of endur ance under the action of weather and other forces can not be readily determined. The external aspect of the stone may fail to give any clue to it; nor can all the tests we yet know determine to a certainty, in the laboratory, just how a given rock will withstand the effect of our variable climate and the gases of our cities. If our land were what is known as a rainless country, and if the temperature were uniform throughout the year, the selection of a durable building stone would be much simplified. The cities of northern Europe are full of failures in the stones of important structures. The most costly building erected in modern times, perhaps the most costly edifice reared since the Great Pyramid,—the Parliament House in London,—was built of a stone taken on the recommendation of a committee representing the best scientific and technical skill of Great Britain. The stone selected was submitted to various tests, but the corroding influence of the London atmosphere was overlooked. The great structure was built, and now it seems questionable whether it can be made to endure as long as a timber building would stand, so great is the effect of the gases of the atmosphere upon the stone. This is only one of the numerous instances that might be cited in which a neglect to consider the climatic conditions of a particular locality in selecting a building material has proved disastrous.
"The great difference which may exist in the durability of stones of the same kind, presenting little, difference in appearance, is strik ingly exemplified at Oxford, England, where Christ Church Cathedral, built in the twelfth or thirteenth century of oolite from a quarry about fifteen miles away, is in good preservation, while many colleges only two or three centuries old, built also of odlite from a quarry in the neighborhood of Oxford, are rapidly crumbling to pieces."* The strength of stone is in some instances a cardi nal quality, as when it is to form piers or columns to support great weights, or lintels that span considerable intervals. It is also an indispensable attribute of stone that is to be exposed to mechanical violence or unusual wear, as in steps, sills, jambs, etc.
This element is of more importance to the architect than to the engineer; and yet the latter can not afford to neglect entirely the element of beauty in the design of his most utilitarian structures. The stone should have a durable and pleasing color.