a derrick was erected thereon, and the tracks were used for cars to receive the excavated material hoisted from sub-grade.  The disposal trestle was maintained in this position until such time as it would interfere with the excavation, and then the tracks were abandoned.  This was done on November 11th, 1908.  Fig. 3, Plate L, shows the finishing of the excavation on the north side of the work.  On August 30th, 1908, a cut was made under Ninth Avenue at sub-grade, and cars could then be run from Seventh to Tenth Avenue at sub-grade.  On October 24th, 1908, the connection with the disposal trestle east of Ninth Avenue was abandoned, and all excavated material was hoisted from sub-grade at Tenth Avenue by derricks.

As previously stated, the contractor was required to make complete disposal of all excavated material after January 1st, 1909, but was allowed the use of the pier until January 20th, 1909, after which date the materials were hoisted by derricks at Tenth Avenue, loaded on 2-horse trucks, and transported to the 30th Street pier, North River, where it was loaded on scows by two electric derricks.  A considerable amount of the rock excavation was broken up and used for back-fill.

Earth Excavation.—­Practically all the earth excavation, amounting to about 57,000 cu, yd., was done with steam shovels.  The average quantity of earth excavated by a steam shovel per 10-hour shift was 180 cu. yd.  This material was loaded on side-dump cars and taken to the disposal pier where it was dumped through chutes to the decks of scows.  Inasmuch as the quantity of earth excavation was small, as compared with the rock, the earth was used principally for the first layer on the scows for padding, so that small stones might be dumped through the chutes without injuring the decks.

Rock Excavation.—­As previously stated, the rock broke better on the south than on the north side, where there were several slides, and considerable excavation had to be taken out beyond the neat line required in the specifications.  The worst slide occurred at midnight on July 3d, 1909, at about Station 188 + 50.  The last blast, to complete the excavation to sub-grade at this point, had been fired in the afternoon of the same day, and the mucking was practically completed.  Great care had been taken in excavating near this point, as it was evident that the rock was not of a very stable character, but, when the excavation had been completed, it was thought that the rock remaining in place would stand.  The volume of material brought down by this slide amounted to about 200 cu. yd.  The rock on the south side broke very well, and there were no slides of any consequence.

The drill holes were laid out by the blaster, and the general method of drilling for different classes of work was as follows:  In breaking down, the holes were started about 8 ft. apart, on a slight batter, so that at the bottom they would be considerably less than 8 ft. apart.  They were drilled about 10 ft. deep, and blasting logs were used, as it was necessary to load quite heavily in order to lift the material and start the cut.  After the cut had been made, side holes were shot to widen out sufficiently to start another cut.