STONE SIDEWALKS. One of the earliest methods of pav ing foot-ways was to cover them with natural stone flagging, and such walks are still very common where flagstones of suitable size may be readily obtained. If hard and smooth and well laid, nat ural stone slabs make a fairly durable and satisfactory walk. A walk made of split flagstones is ordinarily a little smoother than one made of brick, but is not so smooth as a cement walk. If the stone is tool-dressed, it may be nearly or quite as smooth as a cement walk.
Granite, limestone, and sandstone are often used. The kind of stone to be employed in any particular locality will depend upon the availability of the stone and the service required of it.
On business streets where large blocks are required to span coal or storage vaults under the sidewalk, and where large loads are likely to be transported over it from the curb to the building, gran ite is generally used; but it is expensive, and wears slippery, so that when laid upon a crowded business street its surface must fre quently be roughened to prevent its becoming dangerously slip pery. It is largely used in the eastern cities where cheap water transportation can be had. Sandstone, when sufficiently hard to resist abrasion satisfactorily, makes the best flagstones. since its gritty nature prevents it from wearing slippery. In and around New York city, Hudson River bluestone, a variety of sandstone (see § 517), is much used for this purpose. In the west, Bedford (Ind.) limestone is employed, although it chips and spalls too easy for the best results.
On residence streets, the flagstones are laid upon the natural soil or upon a foundation of cinders or gravel. If laid directly upon the soil, the stones are likely to become displaced by the ac tion of frost; and therefore they should be laid upon a sand cushion resting on a well-rammed bed of porous gravel or cinders, and should be carefully bedded so as to preserve a uniform surface.
The flagstones should be as large as is consistent with economy, since there will then be fewer joints and less likelihood of the sur face of the walk becoming uneven. On the other hand, if the size
be made too great, the cost will be excessive, as it is more expensive to quarry and to transport large blocks than small ones, and there is also more likelihood of breakage. As a rule the stones should not contain less than 15 or 16 square feet, although blocks 1i by 21 feet are not uncommon. The thickness of the flagstones for walks on residence streets laid upon a solid foundation usually varies from 2 to 3 inches. The edges should be cut straight and square, and smooth enough to lay thin joints. The stones should be laid with their length across the walk to prevent pedestrians from walking ,along the middle of a row of stones and wearing them hollow; and the stones should break joints, so as to prevent continuous longitudinal joints.
The ends of the stones should be cut on a bevel so that there may be no joints in the direction of the travel. The best arrange ment of the end joints is shown in Fig. 162, page 622. Not infre quently the joints all slope toward one end of the crossing, in which case some of them are parallel to the traffic going around the corner, and hence this arrangement is not so good as the one shown in Fig. 162. It is usually specified that the ends shall be dressed to lay }-inch joints for the full thickness of the stone, and that the upper surface shall be dressed so as to have no depressions of more than inch. The stones should be firmly bedded upon the foundation.
In New York city, Hudson River bluestone sidewalk flags cost from 16 to 22 cents per square foot delivered on the street, and the cost of laying is about 21 to 3 cents per square foot. In Bos ton, Hudson River bluestone crossings cost 29 to 30 cents per square foot f. o. b. the wharf, and cost about 2 cents to haul to the street.