You are describing a "joist", but are you looking at and talking about the sill of the foundation? IF this is a big, thicker than the floor joists board that is sitting on the brick which is sitting on top of the concrete wall, then it sounds like the sill. IF it is the sill, it can be changed out. It's not the easiest job to do but can be done. The trick is to jack the existing floor joists up evenly and slowly to take the weight off of the existing sill. Then the sill can be cut into sections for removal. Size up the sill before removal and have your new material ready to replace immediately. I replace sill in sections with the joints between the existing floor joist.