 The underlying geology of Islay is intricate for such a small area.The deformed Palaeoproterozoic igneous rock of the Rhinns complex is dominated by a coarse-grained gneiss cut by large intrusions of deformed gabbro.Once thought to be part of the Lewisian complex, it lies beneath the Colonsay Group of metasedimentary rocks that forms the bedrock at the northern end of the Rinns.