Nearly all granites are suitable for this work, but Carnarvonshire syenite[57] is said to be the best material that can be used, although, being denser than granite, it is heavier and consequently more expensive.
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.
| Name of stone. | Super- ficial area in feet. | Original weight. | Loss of weight by wear. | Loss per super- ficial foot. | Relative 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.
One of the first really good granite pavements introduced into London was that known as the “Euston Pavement,” and it was constructed in the following manner: The foundation was shaped to the intended surface of the finished roadway; upon this a layer of coarse gravel was spread 4 inches in thickness, this was well rammed,[61] and upon it was spread 4 inches of gravel mixed with a small quantity of chalk to bind it; this again being well rammed, upon it was placed a similar layer only composed of finer gravel, and upon this foundation the stones were placed, being bedded upon about an inch of fine sand. The stones used were Mount Sorrel granite, which were hammer-dressed and squared, 3 inches in width by 4 inches in depth; they were set close together at right angles with the lines of the kerb, they were then thoroughly rammed by the pavior. The whole surface was afterwards covered with screened gravel which was allowed to find its way into the joints and thus steady the entire pavement.