A second signal tower 126 feet high, and capable of being made 40 feet higher, was built on the right flank of the line, on the high bluff known as "Crow's Nest," James River, opposite Aiken's. From the top of this could be seen the Richmond and Petersburg turnpike and the cross-roads connecting the main roads which ran to Richmond on the north side of the James River. A lookout constantly stationed here gave information of the enemy's movements.
Major-General Butler having conceived the idea of cutting a canal across the peninsula known as Dutch Gap, to pass iron-clads and other war vessels through to avoid Trent's Reach and the Howlett Battery, and the idea receiving the warm support of the then commander of the navy in the river, a survey of the locality was made by his direction.
From the sketch given below it will be seen that the river widens from 400 feet at the Howlett house to 2,700 at Trent's Reach. As a consequence, at the latter place the channel becomes narrower and shallower, and at ordinary high water vessels drawing twelve feet ten inches of water can pass under favorable circumstances, but the channel was effectually blocked by the powerful battery (Dantzler) at the Howlett house, which had a plunging fire upon the whole channel from Trent's Reach up to within a few hundred yards of the Howlett house. This battery had also embrasures cut to look up the river, to give a fire in rear in case any vessel was successful in passing the heavy fire of its front.
The survey of Dutch Gap showed a center section line 552 feet long, from a point in the channel on the south to a point in the channel on the north, 15 feet deep. The highest point on this center line was 38.5 feet above high-water mark, and the lowest 4 feet, which was at the south mouth. On a line 60 feet from this center line, on either side, the ground rose to 42,8 feet at the north mouth, and to 11.4 feet on the south. The difference of water level was 10.1 inches, taken at extreme low tide, thus showing the natural fall of the river between these points to be 2.13 inches to the mile. To all appearances the soil offered no insuperable difficulties for excavation, although it was rumored that the James River granite, which outcropped a mile above the lower mouth and a mile and a half below, would be met with beneath the upper strata and cause a complete failure.
The strata met with were as follows, viz: Yellow Virginia brick clay for twelve feet; layer of coarse sand and gravel, two to four feet; half an inch to two inches bog-iron ore; layer of pebbles and large gravel, two feet; then hard blue clay, or hardpan, containing a large quantity of sulphured of iron or iron pyrites. This latter stratum was never exhausted, and the bottom and sides of the canal were chiseled out of this, presenting as smooth and compact a surface as if built with masonry. In round numbers, there were about 48,000 cubic yards to be excavated-the canal to be sixty feet wide at high water, forty feet wide at bottom,and fifteen feet deep.
It is a question whether this project-one of the simplest in civil engineering-would have been of any advantage other than to bring our navy a few miles farther up the river; for after it was commenced it was well known that other and nearly as powerful batteries lined both bakes of the James River, commanding almost impassable obstacles, and ready to do their share in disputing the passage to the rebel capital. And besides, it was an ascertained fact that the river was filled with torpedoes of the most delicate construction of three of our vessels