The geology of the neighbourhoods of Flint, Mold, and Ruthin ...

PREFACE.
TnE first edition of the Quarter-sheet of the Maps of the Geo-
logical Survey (79 S.E.) described in the present Memoir was
published in 1850, and was revised up to 1855. The western
portion was principally mapped by Mr. W. T. Aveline, the Coal-
Measures by Mr. D. H. Williams, and the New Red Sandstone
by Professor E. Hull, while the lodes were inserted by Sir W. W.
Smyth. The materials for the present Memoir were collected
during a re-survey by Messrs. 0. E. De Ranee and A. Strahan,
made on the six-inch scale, when the boundaries of the Glacial
and other superficial deposits were traced for the first time. The
eastern part of the Quarter-sheet, comprising the New Red Sand-
stone and the Flintshire Coal-field (exclusive of the Leeswood
district), was re-surveyed by Mr. De Ranee, the remainder of the
map by Mr. Strahan. Quarter-sheet 79 S.E. (Old Series) covers
nearly the same area as Sheet 108 (New Series). The limits of
the latter lie about half-a-mile further south and further west
than those of the earlier map.
The area represented includes portions of the Vale of Clwyd,
the Estuary of the Dee, and the intervening high ground composed
of Silurian and Lower Carboniferous Rocks.
Considerable changes have been made in the mapping of the
Vale of Clwyd. The Trias, formerly believed to overlap the Car-
boniferous rocks, and to pass on to the Wenlock Shale, is now
shown to be affected by a great fault, which throws down both
Carboniferous and Triassic strata along the western flanks of the
Silurian range. To this dislocation the existence of the outlier
of newer rocks in the Silurian area of North Wales is mainly
due—a structure that forms a striking analogy to that of the
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