...shua railroad—now a part of the Boston & Maine. The latter stands like a sentry, as it were, forbidding the corpse of the old canal it has slain to rise again; yet, even in death, the old Middlesex canal is remembered by its ancient friend, the Merrimac, whose waters ebb and flow in a narrow culvert connecting the river with the shrub-grown valley which marks the bed of the almost forgotten canal.) T...