Question about roof - no shingles? (xpost /r/HomeImprovement)

My wife and I recently purchased a house in Ohio. This is our first home, and we're still learning about everything home-related. I know next-to-nothing about roofs, and a large section of our roof seems to be covered by a material that I think I've ever only seen on flat roofs, and this is on a sloped roof. Is this normal or would there be a reason for this? Was this just a cheap way of fixing a large section of the roof, that's going to cause us problems soon?

Pictures: http://i.imgur.com/jTQnjvz.jpg http://i.imgur.com/5kkiK51.jpg