Although there are still residents, the original town of Marble Rock was a thriving mill town on the Gananoque River, about 6 miles north of the outlet into the St. Lawrence.
Originally settled by William Emery on a 1798 land grant, the Emery family built a wooden dam with sluiceways at both ends; a grist mill on the west bank and a sawmill on the east bank. The mill was sold to James Coleman in 1856, and by 1862 was under the control of William Stone Macdonald of the Gananoque Water Power Company (established by act of parliament March 4th, 1868) and became known as the 'Upper Dam' (They also controlled the dam in Gananoque.)
The original wooden dam was replaced by the new company, and a guard house was built on the east bank to protect the dam from irate farmers. (Flooding of farmlands by dams has historically been responded to with dynamite, thus resoving the flooding problem.) The current dam was built in the early 1920's about 200 feet downstream from the original dams, and is still used for flood control.
The bridge just south of the dam was built in 1923, and was a steel frame with a wooden floor. It collapsed in 1975 when an overweight truck attempted to cross.
I intend to return when it is not pouring rain and the flooding has abated. When it is a little safer to navigate the shore, there is much more to be seen.
Update Sept 2014:
Managed to get down to the shore and looked for the remains of the guard house. Unable to locate it. The shore is difficult to access and is a vertical 50 foot cliff in most places.