I found a bottle fragment at an old farmstead dating about 1920-1945, in the Houston, Texas area. There's not enough there to identify it, just some vertical ribs and a flat space for a product label. The base has the O in a square maker's mark for Owen's glass, which dates it to 1919-1929. What's unusual about this bottle is that the base has a rectangular indented slot. Does anyone know what the purpose of that slot would be? And would that possibly identify the fragment?