SQ^! REPORT — 1898 



and tlie fact that the coalfields of Durham, Northumberland, Yorkshire, and 

 Lancashire had been for the most part geologically surveyed on the 6-inch scale, 

 he would give directions that the geological survey of the mineral districts of 

 South Wales and Monmouthshire should be immediately taken in hand and 

 vigorously prosecuted on that scale. Answer was made that it would be arranged 

 with the Director-General that tlie survey should be commenced as soon as possible 

 and prosecuted as vigorously as the size of the disposable staff of the surveyors and 

 the exigencies of the other branches of the work would allow. The revision was 

 commenced five weeks later, and its progress up to date forms the subject of the 

 following note. 



Until the year 1893 I was engaged alone upon the revision, hut in that year I 

 was joined by Mr. W. Gibson, in 1894 by Mr. J. R. Dakyns, and in 1895 by Mr. 

 R. H. Tiddeman. In 1896 Mr. Dakyns retired, and his place was taken by Mr. 

 T. C. Cantrill. 



The area over which the revision will extend is embraced in the New Series 

 1-inch Ordnance Maps, 226-232, 244-249, 261-263, sixteen sheets altogether, and 

 amounts to a little over 2,000 square miles. Of these, three sheets (249, 232, 263) 

 have been published, one (248) is being engraved, while the surveying of two 

 more (231, 262) is nearly complete. The total area surveyed by the end of 1897 

 amounted to 1,006 square miles, in which 5,011 miles of geological lines had been 

 traced upon the maps. 



The work is engraved on the 1-inch New Series Ordnance Maps only, but 

 the lines are all traced in the field on the 6-inch maps. Clean copies of these 

 working maps are deposited in the Office, and can be consulted or copied as soon 

 as the corresponding 1-inch sheet is published. At the same time sheets of 

 vertical sections illustratintr the Coal Measures are prepared: two of these, giving 

 cseries of shaft-sections in Monmouthshire and Eastern Glamorganshire, have been 

 published, and others are in preparation. Explanations to accompany each sheet 

 of the map are also being written: in these the local geology will be briefly 

 explained; but it is proposed to describe the Coal-field as a whole in a separate 

 volume when the revision is complete. 



I take this opportunity of acknowledging, on behalf of my colleagues and 

 myself, the invaluable assistance which we have received from the managers, 

 engineers, and surveyors in our work in the Coal-field. Without such aid the 

 mapping would have been impossible, and the unvarying courtesy with which it 

 was rendered has greatly facilitated a task that was far from easy. Of the 

 important information recorded in the ' Proceedings ' of the South Wales Institute 

 of Engineers, and the Cardifl:' Natural History Society also, we have freely availed 

 ourselves, acknowledgment of all of which will be made in due course. 



In order that the map of the Coal-field should present the structure as cod- 

 -spicuously as possible, it was necessaiy to subdivide the great mass of Coal 

 Measures which had been represented by one tint only on the old map. At tlie 

 eastern end of the field it was apparent that a suitable threefold division of the 

 strata held good, the three divisions not only differing in their mineral contents, 

 but presenting such physical features as lent themselves to the purposes of the 

 geological surveyor. I wish, however, to point out that no correlation is intended 

 Avith the Upper, Middle, and Lower Coal Measures of other fields. Not only is it 

 extremely Improbable that any representatives of the Upper Coal Measures exist, 

 but it is an open question how much of the Middle Coal ^Measures are present in 

 South Wales. The subdivisions referred to consist of — 



1. An upper series of shales and felspathic sandstones with a few thin seams of 

 coal and ironstone. The sandstones are often indistinguishable from Pennant, but 

 the series is softer on the whole and forms cultivated land of flowing contour. 

 Tor its base the Mynyddlslwyn Vein, a valuable and constant house-coal, served 

 conveniently. 



2. The ]?eunant Series, which in Monmouthshire is made up almost wholly of 

 hard current-bedded highly felspathic grit with a few thin and impersistent coal 

 .seams. This series forms uncultivated moorlands, intersected by deep valleys 



