The roadway where stone tramways are employed cannot be of convex section; on the contrary, it should be concave, with the channel, gutter, or water table in the centre. This is in itself an obvious advantage, and I trust that the question of these tramways may at some future date receive more attention from English engineers; the great objection to them in this country being that the smooth tram-track would be very slippery and apt to throw horses down when passing on and off, but they have many advantages which should not be passed over without consideration.[66] [53] Birmingham in 1854 had not, I believe, a single mile of paved streets; the principal ones are now nearly all paved with granite setts, and over 20,000 square yards were so paved in 1880. [54] It is said that the cost per annum per square yard of granite paved roadways is but 3_d._, whereas the same cost for macadamised roadways under the same circumstances is 1_s._ 6_d._ [55] In Paris after considerable research into the question, the engineers of the Ponts et Chausseés, decided that the size of the paving stones, which used formerly to be 9 inches square should be 4 inches wide by 6¹⁄₄ inches long by 6¹⁄₄ inches deep, the stone that is used being a grit sandstone, from the forest of Fontainebleu. [56] _Vide_ ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 66. [57] Syenite is a hard, greenish-grey metamorphic rock, composed principally of silica, alumina, and lime, in conjunction with magnesia, iron, etc. Its specific gravity is 2·96. [58] Mr. Boyle, District Surveyor of Manchester, says: “I would caution you against the use of the old blue Penmaenmawr stone as being an extremely slippery stone, and one which makes a dangerous pavement.” _Vide_ ‘Proceedings of the Association of Municipal and Sanitary Engineers,’ vol. iii. p. 58. [59] The old granite paving of London used only to last eight years. _Vide_ ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. ix. p. 222. [60] _Vide_ ‘Street Carriageway Pavements,’ by George Frederick Deacon, M. Inst. C.E., ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. lviii. p. 1 _et seq._ [61] The pavior’s rammer is about 55 lb. in weight, with an iron ring at its foot; this is swung with some dexterity between the legs, and is allowed to fall with great force upon the earth or stones it is in use upon.