The Interesting Life of Buildings (part 2)

Following on from my posting a week ago (which can be found here) I've managed to get a picture of another building that's interesting and nearby (see above)

This one is the annex on the side of St Mary's Catholic Church in Bradford.

What intrigues me, is the colour around the window in the middle of the picture. Now, I'm assuming that the window was replaced at some point (which explains the different colour stone) but the size of the area that was replaced, well, why* ?


*Exploding priests ?
*Really dodgy builder ?