[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.
[62] The usual specifications for the Guidet paving blocks (in New York) require that they shall be of granite, equal in hardness to the Quincy granite, of durable and uniform quality, each measuring not less than 3¹⁄₂ nor more than 4¹⁄₂ inches in width on the upper surface or face, and not less than 10 nor more than 15 inches in length, and not less than 8 nor more than 9 inches in depth. Blocks of 3¹⁄₂ inches in width on the face to be not less than 3 inches in width at the base; all other blocks to measure on the base not more than 1 inch less in width or in length than on the face. The blocks are set upright in close contact on their edges in courses, with the longest dimensions and the continuous joints running across the street, breaking joints lengthwise of the street.
The ends of the blocks are dressed off so as to give close joints in the direction of the draught, while the broad vertical sides of the blocks are left rugged or uneven, or with the split rock-face so that the continuous joints running across the street are somewhat open. Vide ‘Roads, Streets, and Pavements’ by Q. A. Gillmore, p. 157.
[63] Vide ‘A Treatise on Roads,’ by Sir Henry Parnell, p. 130.
[64] As these ingredients often vary very much in their constitution, the surveyor must use his judgment to a great extent as to these proportions.