Architect Alfred Waterhouse made his mark on the city in designing the Manchester University complex, the Refuge Assurance Building, Strangeways Prison Tower and the Town Hall. Finished in 1887 and built primarily in a mix of gothic styles, Manchester Town Hall used dun-coloured, durable Spinkwell sandstone from Bradford, Yorkshire because although the prevailing trend was to build using a polychromous mix of stone, the pragmatic Waterhouse realised that Manchester buildings were rapidly coated in velvety black soot from the heavily polluted atmosphere and so outward colour mattered little. Such a huge building necessitated the provision of an enormous 500,000 feet of stone, as well as 14 million bricks, 17,000 foot of granite shafting, and 68,000 ft of polished oak. In the latter stages of its construction, over 700 stonemasons were working the stone. Inside the building, granites from three locations within the British Isles have been used to create distinctive spiral staircases; the English, Scottish and Irish staircases. Granite is an igneous rock, originating as a molten magma from within the Earth’s mantle, the layer below the Crust. Forced upwards towards the Earth’s surface, the magma cooled slowly within the crust rather than being erupted as lava at the surface, a gradual solidification that allowed the characteristic large crystals seen within granite to form. The detail photo of the English staircase column shows such large crystals (termed phenocrysts) of the pink mineral orthoclase feldspar, characteristic of granite from Shap, in the English Lake District.