Page:Economic History of Virginia Vol 1.djvu/131

 channel here was narrow enough to be defended by so small and short-ranged a piece of ordnance as the sacre. The strategic advantages of the general locality were early recognized. Fort Algernon has been replaced in modern times by Fortress Monroe, which is likely to be maintained indefinitely unless there is a greater revolution in the methods of marine warfare than has been foreshadowed by inventions in the past. The channel at the mouth of the Nansemond was only three fathoms in depth, and extensive shoals offered serious obstruction to entrance into the Rappahannock. The York, a magnificent body of water, which, if situated in the Old World, would have long ago been celebrated in song and romance, was, unlike the Powhatan and Rappahannock, the two greatest of its fellows with the exception of the Potomac, distinguished for a deep channel where it emptied into the Bay, but this was largely due to the contraction of its bed near its mouth; it offered a marked difference in this respect from the other great rivers of Virginia, which grew steadily broader as they approached the Chesapeake.

In the vicinity of Jamestown Island, there was a tide and half tide, that is to say, there was a flow for two hours along the line of shore before the ebb was observed in the centre of the stream. The flux and reflux under the influence of the sea extended to the foot of the Falls of the Powhatan, the rise in the water between the Falls