The Southern Uplands contain 10 or more distinct deep-water stratigraphic sequences consisting of basalt and chert and/or graptolitic shale, below thick greywackes. These sequences are separated by major reverse strike faults. Adjacent sequences differ in sedimentary characteristics and age, indicating that they were originally deposited far apart. Within each fault-bounded tract the individual sequences are disrupted and repeated by further, less important, strike faults and by folding. In the N (away from the site of the Iapetus Ocean) the sequences are older than in the S, but the majority of the beds within each sequence young to the N. This structure is compared with modern accretionary prisms, which develop on active continental margins where the oceanic plate has a thick sedimentary cover.