The particulars given in Table LII. show in a comprehensive manner the class of wood used and the method adopted in forming the joints in laying wood pavements in the principal cities and towns in the kingdom, with the cost and amount of annual repairs and the life of the paving blocks so far as can be obtained. The towns are arranged according to the population.

482. From the figures given in the preceding table it appears that the average life of soft wood paving in the busiest thoroughfares in London is about 6 years, and for Australian hard woods, which are not worn out yet, it is estimated at ten years. The cost of paving, assuming the existing foundations to be sufficient, is 8s. for deal, and 11s. for Australian hard woods per square yard.

The annual expenditure for repairs during the lifetime of the pavement must necessarily be a variable item, although it must obviously be less for hard wood paving, but in the following calculation it may be assumed to be the same in order to allow of comparisons.

The relative wear and annual cost of pavements, taking the life or service of soft wood at seven years, and Western Australian hard woods at twelve years, exclusive of annual repairs and cleansing, will therefore be as follows.

This clearly shows a saving in favour of hard woods, and that economy may be effected by paying a higher price for a more durable material, as also that a hard wood pavement with twelve years' life, estimated by wear, is equivalent to a soft wood pavement having seven years' service.

Table LIII. gives the total expenditure and amount of the average annual payments on the first cost of the work, but exclusive of foundations, repairs, and cleansing, for soft and hard wood pavements on a carriageway 1 mile long and 40 feet wide.

If the repairs and cleansing be taken into account there can be no doubt as to there being a further considerable annual saving in the case of hard wood, and although the first cost is greater, hard wood pavements are less expensive in the long run, particularly where vehicular traffic is heavy. In addition to this there is a considerable advantage, especially in busy carriageways, of the thoroughfare being less frequently closed for renewals, which is a matter of great importance to business people, shopkeepers and others.

CHAPTER XI.

ASPHALTE PAVEMENTS.

483. Asphalte pavements for carriageways were introduced into London in 1869, having been used in Paris as early as 1854, where their application became general in 1867.

The principal sources of supply of bituminous or asphaltic rock, which is a natural stone consisting of fine carbonate of lime impregnated with bitumen or mineral pitch of a liver brown colour, are Val de Travers, in Switzerland; Seyssel, in France; Limmer, in Hanover; and also some Sicilian mines. The pitch lake in Trinidad supplies the bitumen from which the best artificial asphaltes are made.

The asphalte chiefly used for carriageway pavements in Europe has hitherto been obtained from Val de Travers and Limmer; that made from Trinidad pitch, although more or less a failure when first introduced into this country, is now being extensively laid in London, and that it is the composition best suited for withstanding the heavy and continuous wheel traffic and climate appears now to have been satisfactorily determined.

484. In Canada and the United States, Trinidad asphalte only is used in the principal cities and towns; over 30 million square yards have been laid, the length of carriageways so paved being approximately 2000 miles.

It appears strange to remark, as already observed, that the earlier Trinidad asphaltic pavements in Europe were not successful, and also that the thoroughfares laid in Washington, U.S.A., made from European bituminous. limestone, were likewise failures.

The latter kind of pavement, laid in Pennsylvania Avenue and other thoroughfares in Washington, was, after a few years' wear, replaced by Trinidad lake asphalte, which has remained for a considerable period of time in an efficient and smooth condition.

485. These pavements are now laid only in a compressed form, mastic asphalte (as generally understood), which was used for carriageways at one time, being now a thing of the past. In the bituminous rock pavements the material is first broken to about 3-inch cubes, then pulverized by being

passed through a disintegrator and reduced to a fine powder, which will pass through a sieve having a mesh equal to 0.10 of an inch. In this condition it is ready for use, but it has to be heated before being applied to form the street covering.

In the case of Trinidad asphalte, the crude bitumen obtained from the pitch lake is refined so as to eliminate the water and vegetable matter contained in it. This refined bitumen, which becomes hard when cool, is converted into 'asphaltic cement,' by adding a small quantity of residuum oil of petroleum, which gives the mixture a certain amount of plasticity. This, added to sand and powdered limestone, forms the asphaltic composition. It cements these ingredients together when mixed hot, the proportions being regulated according to the quality of the asphaltic cement' and the character of the sand; if this is of a suitable nature, the limestone dust is dispensed with altogether. The climate of the particular town in which the pavement is to be laid has also a considerable influence on the relative proportions of the ingredients in the mixture.

Generally the proportions may be taken as follows:

486. Contour and Gradients.-As asphalte pavements are extremely smooth, surface water is easily drained from the thoroughfare; consequently, an excessive rise, or even the amount generally given to a pitched or wooden pavement, is unnecessary, a rise of about to 10 of the width of the carriageway being in most circumstances sufficient. It is not advisable to lay a limestone rock asphalte pavement steeper than 1 in 50 or 1 in 60, aud Trinidad asphalte 1 in 25. On steeper gradients they afford but little foothold for horses, and are consequently not safe to travel over.

487. Foundations.-A solid unyielding foundation is indispensable for all asphaltic pavements. It should be laid in a similar manner to that described for a pitched or wooden pavement. Considering that the thickness of the asphalte is only about 2 inches, it is essential that the concrete be of first rate quality; while in some cases the depth may be advantageously increased to 9 inches to the desired contour, and floated with cement mortar.

488. Compressed asphalte has hitherto been the name applied to bituminous limestone rocks which are reduced to a powder, then laid on the concrete foundation, rammed with punners and subsequently rolled until thoroughly compressed. Trinidad asphalte is treated in a similar manner by being compressed first with light rollers, and subsequently with heavier ones. Specifications now generally state that the work is to be of rock