limestone cap, to Nicollet Island. In October 4, 1869 a hole in the limestone cap over the tunnel broke through as the tunnel neared Nicollet Island. The torrent of water blasted Hennepin Island and threatened to destroy the falls. Attempts to plug the hole were partially successful. The fix was a concrete dike (wall) built by the Corps of Engineers just upstream from the falls all the way across the river from just under the limestone cap down as much as 40 feet (12 m). Progression of the falls upstream was a separate problem, and was stopped by the Corps finishing a wooden apron (later replaced by concrete) creating a spillway to protect the edge of the falls and underlying sandstone. The Corps also built low dams above the falls to keep the limestone wet, as drying increased weathering. This work assisted by the Corps was eventually completed in 1884. The federal government spent $615,000 on this effort, while the two cities spent $334,500. Possibly as a result of the bonding needed to rehabilitate the falls, the cities of St. Anthony and Minneapolis merged on April 9, 1872. Development of flour milling The St. Anthony Express newspaper predicted in 1855 that, "The time is not distant when Minnesota, with the superiority of her soil and seasons for wheat culture, and her unparalleled water power for manufacturing flour, will export largely of this article. ... our mills will turn out wheat, superior in quality and appearance to any now manufactured in the West." By 1876, eighteen flour mills had been built on the west side of the river below the falls. The first mills used traditional technology of millstones that would pulverize the grain and grind as much flour as possible in one pass. This system worked best for winter wheat, which was sown in the fall and resumed its growth in the spring. However, the harsh winter conditions of the upper Midwest did not lend themselves to the production of winter wheat, since the deep frosts and lack of snow cover killed the crop. Spring wheat, which could be sown in the spring and reaped in the summer, was a more dependable crop. However, conventional milling techniques did not produce a desirable product, since the harder husks of spring wheat kernels fractured between the grindstones. The gluten and starch in the flour could not be mixed completely, either, and the