The Lower Palaeozoic time-scale is discussed in the light of a new date for the Threlkeld Microgranite and a reassessment of other published dates from the Lake District which suggest ages of c. 410 Ma for the base of the Devonian; c. 421 Ma for the Ashgill; c. 429 Ma for the late Caradoc; c. 439 Ma for the early Llandeilo, and c. 468 Ma for the early Llanvirn.
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Christopher Rundle (1981) studied this question.
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