varied from granite to mica schist. It was made up of quartz, feldspar, and
mica, and there were also some isolated specimens of pyrites, hornblend,
tourmaline, and serpentine. On the south side of the work, just west of
Ninth Avenue, there were excellent examples of "contortions" of veins of
quartz in the darker rock. On the east side of Ninth Avenue, near the north
end of the work, glacial marks were found on the rock surface. The general
direction of the stratification was north 5° west, and the general incline
about 60° with the horizontal. As a rule, the rock broke sharply along the
line of stratification. On the south side it broke better than on the north
side, where it was usually softer and more likely to slide; and this,
together with the fact that in winter it was subject to alternate freezing
and thawing and in summer to the direct rays of the sun, made it rather
difficult to get a good foundation for the retaining walls.


WORK IN AND UNDER NINTH AVENUE.

_General Description._--The work involved the excavation of about 375 ft.
of the full width of Ninth Avenue to an average depth of about 58 ft., and
the construction over this area of a steel viaduct, the deck of which was
about 24 ft. below the surface, for the ultimate support of the Ninth
Avenue structures.

The following estimated quantities appear in the contract: Excavation of
rock, 72,600 cu. yd.; excavation of all materials except rock, 9,300 cu.
yd.; concrete (1:3:6) in abutments, etc., 1,680 cu. yd.; timber, 504,000
ft., B.M.; structural steel, 1,320,000 lb., etc.

While this excavation was being done it was necessary to support and
maintain the three-track elevated railway structure of the Interborough