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| An angle of Fort Hell (Sedgwick) showing Gabions, Chevaux-de-frise, Abatis and Fraise. From a Photograph. |
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inches square on the end. Five continuous lines of these were laid on the boats two feet ten inches apart.
The flooring of the bridge, called chesses, consisted of boards having a uniform length of fourteen feet, a width of twelve inches, and a thickness of one and a half inches.
To secure the chesses in place, side-rails of about the same dimensions as the balks were laid upon them over the outer balks, to which the rails were fastened by cords known as rack-lashings.
The distance between the centres of two boats in position is called a bay. The distance between the boats is thirteen feet ten inches. The distance between the side-rails is eleven feet, this being the width of the roadway.
An abutment had to be constructed at either end of a
bridge, which was generally done by settling a heavy timber horizontally in the ground, level with the top of the bridge, confining it there by stakes.
A proper approach was then made to this, sometimes by grading, sometimes by corduroying, sometimes by cutting away the bank.
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