not seem to be good practice, as it does not give as good a foothold to the horses, nor will the blocks wear as well as if their courses are at right angles to the street, and this method is almost universally adopted at the present time. A portion of Devonshire Street, Boston, is now paved with blocks in diagonal courses. Originally the right angle method was continued across all inter

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FIG. 9.

secting streets. This was all right for travel on the street being paved, but it was all wrong for the cross-streets, as then it brought the traffic parallel with the blocks, and they soon became unduly worn on the edges and the pavement became rough. This method is shown in Fig. 9. To remove this difficulty the plan shown in Fig. 10 was adopted, in which the courses are run diagonally to the street paved. This obviated the difficulty for half of the intersection, as it brought that portion of the traffic at right angles

to the blocks, as shown by the arrows of the figure, but for the other half of the intersection the traffic remained as before, almost parallel with the blocks. Fig. 11 shows the method which is in use at the present time, and it is as good an arrangement as can be obtained, the principle being to have the traffic, wherever possible, at right angles with the blocks, both on the street proper and at intersections.

The blocks generally should be laid in courses square with the street, stone to stone, and all blocks in the same course to be of uniform width. Too much care cannot be taken in keeping the joints close, as no matter how tight they may seem to be when laid, they will always show up more loosely after being rammed.

Some contractors purchase their blocks by the thousand, others by the yard. In the former case it is to their interest to have a

thousand blocks lay as many yards as possible, and so there is no desire to keep the joints close, or rather there is an inducement for the pavement to be made with large and open joints. In order to prevent this, the specifications of Philadelphia require that the blocks shall be set separately, according to their width, and so that the 31-inch blocks shall lay 32 per square yard, 4 rows to measure

16 inches when laid; 4-inch blocks to lay 28 per square yard, 4 rows to measure 18 inches when laid; 44-inch blocks to lay 25 per square yard, 4 rows to measure 20 inches when laid; and they provide that when these conditions are not complied with a reduction of 25 per cent shall be made from the contract price for such portion of the street as does not conform to the above requirements. It would seem that these restrictions were proper and justifiable. if applied only to the distance a certain number of rows should

measure, but where a variation of 4 inches is allowed in the length, the number per yard will vary according to the length, and it does not seem as if this variation is important.

After the blocks are laid they should be covered with a clean, sharp sand, free from pebbles, which shall be swept or raked into the joints until they are filled; each course should then be set up perpendicular to the surface of the street with proper tools, and all imperfect blocks removed and replaced with good ones, and then the entire surface should be thoroughly rammed. It should then be covered with a second course of sand, treated as before, and rammed the second time. This part of the work should be done with great care. If any soft spot or, as the rammer expresses it, "soft blocks" are found, they should be thoroughly rammed until they are solid and then taken up and the foundation brought to proper grade with added sand, and the blocks replaced and rammed as before. Upon the proper ramming of the pavement depends, in a great measure, how well it will keep its form and shape under traffic. The entire surface of the pavement should be covered with one inch of sand and allowed to remain under traffic a sufficient time to permit all of the joints to be thoroughly filled.

Concrete Foundation.

With this base the subgrade must be treated in the same way as for sand, and the concrete then laid upon it. After the concrete has been completed and set sufficiently so that working upon it will do it no harm, a cushion of sand should be spread over the entire surface. The amount of sand-cushion will depend in a great measure upon the uniformity of the depth of the blocks. If the blocks are of variable depths, the cushion must be deepened, as, on account of the irregularities of the concrete itself, at least 1 inch of sand should be allowed between the bottom of the deepest block and

the concrete.

When a stone-block pavement is laid upon a rigid base, the joints between the blocks should be filled with a substance that will make the pavement, as a whole, water-proof. With a sand base this is not desirable or necessary, as, whatever the joint-filling, the blocks, being set on sand, would always have sufficient motion under traffic to permit water to soak through; but with a concrete

foundation a perfectly water-tight pavement can easily be obtained, and is desirable both from the sanitary and the physical standpoint.

Joint-filling.

Portland Cement.-The first filler that naturally suggested itself, in order to make the pavement rigid, was a mixture of sand and cement. This was a mixture of one part of sand and one of Portland cement, and after the blocks were rammed the joints were poured full of a grout made as above. While making a solid and substantial piece of work at first, the chief objection to this filler is that if for any reason a joint becomes broken it always remains so, and accordingly it has never been used to any great extent in stone pavements.

Ferroid.-In 1886 a filler called "ferroid" was used in Buffalo. This was made up of 10 per cent ferroid, 30 per cent German rock asphalt, 25 per cent Trinidad pitch, 15 per cent coal-tar, and 20 per cent sand. The 10 per cent ferroid above was supposed to be composed of iron borings, sal-ammoniac, and sulphur. This mixture was never very extensively used.

Murphy Grout.-Another joint-filler used to a considerable extent in the West is what is known as " Murphy's Grout Filler." It is principally composed of iron slag and carbonate of lime, and when used on a street a certain proportion of clean, sharp sand is added. This is said to produce a mixture which is as hard as granite and which attaches itself closely to the blocks, making them solid and waterproof.

Tar and Gravel.-The general custom, however, in granite pavements of a concrete base is to fill the joints with gravel and paving-cement. This paving-cement in the vicinity of New York City is composed of 100 lbs. of commercial No. 4 paving-cement, 20 lbs. refined asphalt, and 3 lbs. of residum oil. This commercial paving-cement is made from coal-tar. When coal is distilled for the purpose of making illuminating-gas, one of the important products of the distillation is a liquid called coal-tar. This is a very complex hydrocarbon, which when further distilled produces what is generally known as pitch. Its consistency and exact composition depend upon the amount of distillation to which it has been subjected. It is known to the trade also as paving-cement and numbered according to its hardness. It is much like asphalt