GRANITE AND SANDSTONE BLOCKS.
For the construction of the better class of stone block pavements, blocks of tough granite or sandstone are used, set, in the best work, upon a concrete base, although sometimes placed upon a foundation of sand or gravel.
These pavements when well constructed are about the most satisfactory means yet devised for providing for very heavy traffic, as they present a maximum resistance to wear with a fairly good foothold for horses, and are much more agreeable in service than the old form of rough pavements. There is still much to be desired in the attainment of smoothness and ab sence of noise, and, as a general thing, it may be said that pavements of this kind are desirable only where the weight of traffic is so great that the smoother pave ments would not offer sufficient resistance to wear. Even in such cases it may frequently be questionable whether an additional expense for maintaining a pave ment which would be more pleasant in use and less objectionable to occupants of adjoining premises would not be advisable from an economical as well as from an ęsthetic point of view.
Blocks for stone pavements, in the best work, are cut in the form of parallelopipeds, 9 to 12 inches long, 3 inches wide, and 6 or 7 inches deep. The length should be sufficient to permit the blocks to break joints across the street. The width should be less than that of a horse's hoof in order that the joints in the direction of travel may be close enough together to prevent a horse from slipping in getting a foothold. The depth should
be sufficient to give a bearing surface in the joints large enough to prevent the blocks from tipping when the load comes upon one end of them.
Specifications for granite blocks in New York City in 1908 are as follows: "The blocks to be used shall be of a durable, sound and uniform quality of granite, each stone measuring not less than eight (8) inches, nor more than twelve (12) inches in length; not less than three and one-half (3i) nor more than four and one-half (4i) inches in width, and not less than seven (7) nor more than eight (8) inches in depth, and the stones shall be of the same quality as to hardness, color and grain. No outcrop, soft, brittle or laminated stone will be accepted. The blocks are to be rectangular on top and sides, uniform in thickness, to lay closely, and with fair and true surfaces, free from bunches. Over special construc tions, the blocks may be of dimensions other than above specified when approved by the Engineer. The stone from each quarry shall be piled and laid separately in different sections of the work; and in no case shall the stones from different quarries be mixed."