THE WOOD VARIETIES. Both the hard and the soft varieties of wood have been employed for making paving blocks. The hard woods are used without preservative treatment, and the soft ones are used both with and without preserving (see § 844). In the United States, cedar and cypress, on account of their abundance, cheap ness, and durability against decay, are more generally employed. In Europe nearly all varieties of the pine species have been tried, as well as oak, ash, elm, and gum; but Baltic fir, Indian teak, and Swedish deal seem to be the favorites. Within the past few years, two Australian hard woods, jarrah and karri, have been intro duced in London for paving purposes, and have been favorably received.
None of the woods employed for making paving blocks need a description, except perhaps the Australian hard woods, jarrah and karri.
mersed 48 hours.* Its transverse and crushing strength is about the same as that of English oak and Indian teak.
Karri is interlocked in the grain and is difficult to split; it splinters in breaking and burns with a white ash. It is a little lighter colored than cherry. When seasoned, it has a specific gravity of 1.12, and absorbs about 7 per cent of water when immersed 48 hours. Its transverse strength is a little greater than that of English oak or Indian deal, and its crushing strength is considerably greater.
For street paving, there is little difference between jarrah and karri, although for exceptionally heavy traffic karri shows slightly less wear. Karri shrinks less than jarrah. Both timbers are very plentiful in Western Australia, the trees growing with large, long, straight bodies without limbs. Jarrah and karri are preferred in some vestries of London to any other form of wood paving blocks.