The Devonian of Ferques, (Lower Boulonnais)

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Abstract
Introduction. The Palæozoic rocks of the Boulonnais are classic ground, and received the attention, among others, of De Verneuil, Murchison, Rigaux, and above all Godwin-Austen and Gosselet. Owing to the occurrence of coal, however, most attention has been given to the Carboniferous deposits, and, except for palaeontological work by Rigaux, the Devonian seems to have been comparatively neglected for the last forty years. The classic description is that published by Godwin-Austen in 1853, which has been slightly amended by Gosselet and Rigaux, while the beds have been correlated with those of other areas by Gosselet. The published maps are poor, and of little use in the field. This is partly due to the lack of a good topographical map, but also to the apparent absence of detailed mapping. The accompanying map (Pl. XIV) suffers from the first defect, but was prepared on a scale of 1:1000 over an area extending across the outerop along the Nord Railway, and on a scale of 1:10,000 for the remainder. All the beds are referred to the Upper and to part of the Middle Devonian (Famennian, Frasnian, and Givetian). They consist of limestones, sandstones, shales, dolomites, and conglomerate. Physical Aspect. The Lower Boulonnais may be regarded as forming the southern-most extension of the Weald. It is ringed round by Chalk hills; but the denudation in the centre has been more extensive, exposing a considerable expanse of Jurassic rocks and a smaller one of the Palaeozoic. The district is drained by a number of small

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