This paper is a compilation of published information considered pertinent to the correlation of the 450 Silurian stratigraphic units now recognized in the British Isles. The number of units reflects both the geologic complexity of these islands and the fact that much careful description and geologic mapping was done during the past two centuries. The accompanying bibliography contains more than 800 titles.

Graptolitic facies are widespread in the British Isles, and the graptolitic zonal sequence is used here to form the basis of correlation. In the shelf facies where graptolites are less common, brachiopod lineages are becoming increasingly useful in correlation. Recent work on other groups, particularly conodonts, spores, and ostracodes, provides further bases for correlation.

In early Paleozoic time, Britain and Ireland were traversed by an ocean basin, called the Iapetus Ocean, which in Silurian time, however, provided no barrier to migration as most marine animals are common to both sides. The ocean-floor deposits are characterized by thin, pelagic shale sequences and thick graywacke turbidite sequences, all within the graptolitic facies. Shelf deposits occur along both margins of the ocean, in the Welsh Borderland and Wales on the southeast, and in Scotland and Ireland on the northwest. These shelf areas are characterized by clastic shelly facies with limestone locally developed. Nonmarine deposits are mainly associated with Late Silurian time, just prior to the late phases of the Caledonian orogeny, when all of the British Isles except southwest England became a mountainous, nonmarine area.