Complex sentence: Through the North of England run the Pennines, an upland chain, often referred to as "the backbone of England", which stretches from the Cheviot Hills on the border with Scotland to the Peak District.
Split into simpler sentences: Through the North of England run the Pennines, an upland chain often referred to as "the backbone of England". This stretches from the Cheviot Hills on the border with Scotland to the Peak District.