Foundation. - The depth of subgrade for Bowlder streets shall be sixteen (16) inches below the finished surface of the roadway.

Upon the prepared subgrade, the entire surface of the roadway between the gutters shall be evenly spread with a layer of sound, hard hill limestone, broken into fragments as nearly regular as practicable, which shall measure not more than two and one-half (2 1/2) inches in any direction. The layer shall be of such thickness that, when thoroughly compacted, its surface shall be at a uniform depth of eight (8) inches below the finished roadway grade. The layer shall be compacted by rolling with a steam roller exerting a pressure of not less than two hundred and fifty (250) pounds per lineal inch of roller.

The broken stone shall then be covered with a light layer of gravel and the surface shall be rolled again until thoroughly compact, so as to afford a solid foundation.

Gravel. - Upon the surface of the foundation thus prepared shall be evenly spread a layer of gravel, in which to bed the bowlders, and of such depth as will bring the surface of the paving to the proper grade.

All gravel used on this work must be clean and free from animal or vegetable matter or refuse of any kind, and must not contain more than ten (10) per cent. of clay or loam. Such gravel must not contain pebbles exceeding one (1) inch in diameter in their longest dimensions. The gravel must be of a character which has been found by experience in this locality to be specially adapted for bowlder paving.

Paving. - In paving, the Contractor shall keep the foundation work laid to the proper grade and thoroughly rolled into proper shape at least one hundred (100) feet in advance of the paving, which must be laid in sections of not less than one hundred (100) feet in length, entirely free from gravel, rubbish or covering of any description, and thoroughly swept, ready for inspection.

The bowlders shall be laid from gutter to gutter. They shall be of good shape, free from all flaws or breaks, and shall be of hard, imperishable substance, no sandstone or limestone bowlders to be used, no stone to measure less than four (4) or more than eight (8) inches in longest diameter; the stones to be carefully assorted and so placed that the largest ones shall be next to the gutters. The bowlders when set in an upright position, shall show horizontal dimensions of not less than three (3) nor more than six (6) inches in any direction, and shall be firmly set upon the foundation in a perfectly upright position, with the small ends down and as closely and compactly together as it is possible to set them. When the bowlders have been set for a distance of sixty (60) feet, the first fifty (50) feet must be lightly rammed, after which a covering of gravel, sufficient only to fill the interstices, will be spread over the surface and thoroughly broomed in, and then the whole shall be thoroughly rammed with rammers weighing not less than forty (40) pounds.

As soon as two sections aggregating one hundred and ten (110) feet in length have been thus completed, the first one hundred (100) feet shall be again covered with gravel, broomed and thoroughly rammed, and held ready for inspection.

As soon as each section of one hundred (100) feet has been accepted, a final covering of two (2) inches of gravel shall be spread over its entire surface.

In no case (except where the section terminates the line of work) shall the bowlders be rammed within less than ten (10) feet of the front of the work last laid.

After completion, the surface of the roadway must be true to grade, and must show no continuous lines or unequal settlements.

Payment. - The price bid for bowlder pavement will include the cost of trimming and rolling the subgrade and the furnishing of all labor and material to complete the pavement, including both gravel and broken stone; and will also include all grading for the establishment of the subgrade in cases where no special bid is asked for grading.

Crossings. - Crossings for bowlder streets will consist of strips of granite pavement five (5) feet in width. The crossings will be firmly bedded on the same gravel and broken stone foundation as used for the bowlder paving. The cost of the broken stone and gravel to be included in the price bid for crossings.

Gutters. - The gutters for bowlder streets will consist of strips of granite paving twenty (20) inches in width with a foundation of concrete six (6) inches in depth and twenty-four (24) inches in width. The blocks and all work and material shall conform to the requirements of the specifications for granite pavement, except as follows: The top of the concrete shall be six (6) inches below the grade of the gutter, the blocks shall be bedded on a mortar consisting of one (1) part cement to two (2) parts sand, and with only enough moisture to harden the cement.

The gutter paving should be kept a short distance only in advance of the bowlder paving, and as the latter is finished and rammed, but before the gravel covering is put on, the gutter paving should be finished by pebbling, ramming, filling joints, etc., as specified for granite paving.