Bartholomew Sulivan's geological observations in the Falkland Islands (1838 to 1845) as communicated to Charles Darwin

When in 1846 Charles Darwin published the first account of the geology of the Falkland Islands, he made clear at the beginning that “My examination was confined to the eastern island; but I have received through the kindness of Captain Sulivan and Mr Kent, numerous specimens from the western island, together with copious notes, sufficient to show the almost perfect uniformity of the whole group.” A modern geological map (e.g. Aldiss and Edwards 1999) shows the oldest Falkland Islands rocks to be the ca 1000 million years old, granite and gneiss of the Proterozoic Cape Meredith Complex, which has a very small outcrop on the southernmost point of West Falkland. This ‘basement’ complex is unconformably overlain by the West Falkland Group, a thick succession of marine, near-shore clastic strata ranging in age from Silurian to Carboniferous: a fossiliferous unit in the middle of the group (Fox Bay Formation) can be dated at about 400 million years old. The West Falkland Group underlies most of West Falkland and the northern part of East Falkland. In the southern part of East Falkland a younger succession of strata, the Lafonia Group, has at its base a Permo-Carboniferous glacigenic unit (Fitzroy Tillite Formation) formed about 300 million years ago, which passes upwards into a thick succession of Permian lacustrine strata. The metamorphic and sedimentary rocks are cut by a multitude of Jurassic and Cretaceous dolerite dykes ranging in age between about 180 and 120 million years. The regolith covering the bedrock was largely produced during the last 2 million years or so, by a variety of weathering and periglacial processes, with an extensive peat cover developed over approximately the last 17 000 years.