Discontinuity

On the ridge above the Stowe Valley in Southam is the ruin of an old farmhouse, said to be just about the oldest building in the area. I have always been fascinated by this little farmhouse, and this wall has the most bizarre line of stonework. Why did they lay the courses like this, with such an obvious edge for a fault-line? And why did they think that just one key stone would hold it together?