. Bulletin of the British Museum (Natural History), Geology. 32 COCKS AND D. WORSLEY. Fig. 1 Outcrop map of the Silurian of the Oslo Region, showing the districts mentioned in the text. SHELLY CORRELATION ELEMENTS Stricklandia-Costistricklandia Since Williams (1951), this brachiopod lineage has afforded one of the best means of dating shelly rocks of Lower Silurian age. The earlier parts of the lineage are particularly well documented in the Oslo Region (Baarli 1986) and the later parts, those with Stricklandia laevis and Costistricklandia lirata, are also now known (Baarli & Johnso
. Bulletin of the British Museum (Natural History), Geology. 32 COCKS AND D. WORSLEY. Fig. 1 Outcrop map of the Silurian of the Oslo Region, showing the districts mentioned in the text. SHELLY CORRELATION ELEMENTS Stricklandia-Costistricklandia Since Williams (1951), this brachiopod lineage has afforded one of the best means of dating shelly rocks of Lower Silurian age. The earlier parts of the lineage are particularly well documented in the Oslo Region (Baarli 1986) and the later parts, those with Stricklandia laevis and Costistricklandia lirata, are also now known (Baarli & Johnson 1982, 1988). 5. laevis has previously been recorded from the lower part of the Vik Formation in Asker, MalmOya and Modum and C. lirata from the upper Vik in Asker and the middle Vik and upper Bruflat in the Ringerike district. Baarli & Johnson (1988) also recorded and figured Costistricklandia lirata from the lower Vik Formation in the Skien district. However, the abundant stricklandiids which we have collected in the lower and middle Vik Formation in the Skien, Porsgrunn and Holm- estrand districts (Fig. 7g-i) are identified here as Stricklandia laevis rather than Costistricklandia lirata since there are no substantial ribs and the cardinalia are also typical of that species. This change of identification from that of Baarli & Johnson makes a significant impact on the age deduced for the lower and middle Vik Formation of the southern parts of the Oslo region. We have also found S. lens progressa from the lower part of the Vik Formation in Asker. All these records have been instrumental in forming some of the most useful parameters for our correlation diagram of the area (Fig. 3). Pentamerus-Pentameroides Baarli & Johnson (1982, p. 96) have documented the transi- tion between Pentamerus oblongus and Pentameroides cf. subrectus in beds 12 m above the base of the middle Garnta- ngen member of the Vik Formation at Purk0ya, Ringerike district and Baarli & Johnson
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