together. An 8-in. pipe was then driven forward through the bulkhead for
distances varying from 30 to 100 ft., in order to check the alignment
and grade between the two workings before the shields were actually
shoved together. The errors in the surveys were negligible, but here, as
elsewhere, the shields were not exactly in the desired position, and it
took careful handling to bring the cutting edges together. The Long
Island shields were driven to meet those from Manhattan.

TABLE 2.--RATE OF PROGRESS, NATURE OF MATERIALS, AND METHODS ADOPTED IN
CONSTRUCTION OF EAST RIVER TUNNELS.

LINE A, LONG ISLAND.

--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
All rock |Bottom heading | 69+39.9 | 69+79 |Aug. 2, '06|Sept 25, '06|
| | | | | |
All rock |Center heading | 69+79 | 70+64 |Sept 25, '06|Nov. 21, '06|
| | | | | |
Earth and rock|Center heading | 70+64 | 71+34 |Nov. 21, '06|Dec. 30, '06|
| | | | | |
Earth and rock|Bottom heading | 71+34 | 71+89 |Dec. 30, '06|Feb. 13, '07|
| | | | | |
All rock |Bottom heading | 71+89 | 72+11 |Feb. 13, '07|Feb. 21, '07|
| | | | | |
Earth and rock|Center heading | 72+11 | 72+67 |Feb. 21, '07|Mar. 19, '07|