Everything I do on this 83 year old house turns into an voyage of discovery. This weekends discovery is that about three inches inside the footer is a massive lump of concrete, running about six inches thick. At first I thought it was a second footer. Like they had poured one but realized the house was supposed to be bigger so they poured the second. Probably it is excess concrete scraped off and left in place. If the drain tile was run along the top of the footers there would be only two inches between the top of the drain tile and the floor. A little thin. I considered digging down to full depth between the castings and just putting in gravel wrapped in the landscaping cloth sleeve. Also thought about renting a jackhammer but am afraid how much it will break up the floor nearby by pounding on this layer underneath. Don't want to have to relay the entire floor. So for now, it's hammer drill and hammer time. And slow going.