A desktop resource assessment of building stone and slate on the Island of Bute

Bute has a varied geology, resulting from the presence of the Highland Boundary Fault which crosses the island and brings metamorphic rocks of the Scottish Highlands into contact with Devonian and Carboniferous sedimentary rocks of the Central Belt. The island also has abundant igneous intrusions of various generations, mostly fine-grained, dark basaltic rocks. This diverse geology is reflected in buildings across the island which used local stone and slate, bringing a distinctive character to the built heritage of Bute. Over sixty stone quarries are recorded on Bute. Most of these exploited igneous rock, likely to have been used for roadstone. Large-scale production of building stone was probably limited to Rothesay, where an igneous intrusion at Longhill Quarry provided block for buildings in the town. This ‘greenstone’ was used extensively in buildings up to the mid to late 19th century, when imported sandstone became increasingly used. In rural areas, buildings were typically constructed from the closest available stone type, obtained from any suitable outcrops or small quarries. Dressed stone, sourced from blonde and red sandstone, was also used for early buildings throughout Bute. These sandstones were probably obtained from unrecorded quarries in the Devonian and Carboniferous sediments of the S and E parts of the island.