Rock River, Ill. and Wis. Letter from the Secretary of War, transmitting, with a letter from the Chief of Engineers, reports on preliminary examination and survey of Rock River, with a view to securing a channel 7 feet deep from the dam at the head of the feeder of the Illinois and Mississippi Canal, at or near Sterling, Ill., to the City of Janesville, Wis.; also with a view to ascertaining whether, for the maintenance of navigation, storage reservoirs are necessary at or near the headwaters of said river, and to determine what portion of the cost of said improvement should be borne by owners of water power and others.