Left: American Falls from Goat Island. The back caption says "Goat Island, located half-way between the American and Canadian shores is joined to the American side by a picturesque stone bridge. Night visitors to the island see not only the playing of the lights upon both Falls, but they are best situated to watch the operation of the million candle-power battery of lights which operates from the opposite bank."
Right: The back says "I have just taken an extremely interesting trip through the famous Shredded Wheat Bakeries of the National Biscuit Company here at Niagara Falls. It certainly makes one hungry to see those delicious golden-brown Shredded Wheat Biscuits in the making." (How quaint!)
Middle: Horseshoe Falls of Niagara from the Canadian side. The rear says "The Canadian Falls, which is the larger of the two Falls at Niagara, extends from Goat Island to the Canadian Shore in the general shape of a horseshoe, from which it gets its name.
Bottom: Niagara Falls from Prospect Point. The rear says "The Niagara River leaves Lake Erie at Buffalo at an elevation of about 600 feet above sea level to run a turbulent course for twenty-seven miles to Lake Ontario. In this journey, it descends over 300 feet, 160 feet of descent is made at the falls shown in this picture, located about twenty miles from its source.
None of these has any handwriting, so they are undated. I expect they are from the late 40's or early 50's.