At one time large quantities of paving stones were used in London and Liverpool which were brought from Bombay and China, as ballast for ships trading between those ports. Mount Sorrel from Leicestershire and the Welsh stones are said to wear slippery[58] as well as porphyry, whereas the presence of felspar in the granite always keeps it rough under traffic. Of the granites, that from Dalbeattie in Scotland is said to be the best. The table on the next page, prepared by Mr. Walker in 1831, showing the wear of different stones, may be of interest. TABLE SHOWING THE RESULT OF EXPERIMENTS MADE BY MR. WALKER ON THE WEAR OF STONES IN 1830-31, A PERIOD OF 17 MONTHS. ----------------+-------+---------------+-------+-----------+-------- | Super-| |Loss of| | | ficial| | weight| Loss per | |area in| Original | by |superficial|Relative Name of stone. | feet. | weight. | wear.| foot. | losses. ----------------+-------+---------------+-------+-----------+-------- | |cwt. qrs. lbs.| | | Guernsey | 4·734 | 7 1 12·75| 4·50 | 0·951 | 1·000 Herm | 5·250 | 7 3 24·25| 5·50 | 1·048 | 1·102 Budle | 6·336 | 9 0 15·75| 7·75 | 1·223 | 1·286 Peterhead (blue)| 3·484 | 4 1 7·50| 6·25 | 1·795 | 1·887 Heytor | 4·313 | 6 0 15·25| 8·25 | 1·915 | 2·014 Aberdeen (red) | 5·375 | 7 2 11·50| 11·50 | 2·139 | 2·249 Dartmoor | 4·500 | 6 2 25·0 | 12·50 | 2·778 | 2·921 Aberdeen (blue) | 4·823 | 6 2 16·0 | 14·75 | 3·058 | 3·216 ----------------+-------+---------------+-------+-----------+-------- The Aberdeen granite as at present laid in the City of London, 3 inches wide by 9 inches in depth, has a life of about 15 years.[59] In the City of Durham whinstone setts of the same width last 17 or 18 years, in Manchester similar granite setts last 15 to 20 years. On this subject Mr. Deacon, the then Borough Engineer of Liverpool, has collected some most valuable information, and I refer my readers to a paper read by him before the Institution of Civil Engineers in 1879,[60] for a great deal of useful information on this and other subjects connected with roadways. Various methods have been adopted for constructing granite paved streets, some of which I will proceed to describe.