Complex sentence: Mine spoil was deposited around the early collieries but in the 20th century the Cutacre tip developed in the valley of the Cutacre Clough and was the dumping ground for mine waste from Brackley and neighbouring Mosley Common Collieries.
Split into simpler sentences: Mine spoil was deposited around the early collieries but in the 20th century the Cutacre tip developed in the valley of the Cutacre Clough. In the 20th century was the dumping ground for mine waste from Brackley and neighbouring Mosley Common Collieries.