A. Strahan — Geological Survey of South Wales, etc. 489 



view of the great importance of the South Wales and Monmouth- 

 shire Coalfield, and the 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 the 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, but 

 in that year I was joined by Mr. W. Gibson, in 1894 by Mr. J. E. 

 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 6,011 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 

 illustrating the Coal-measures are prepared : two of these, giving 

 series of shaft-sections in Monmouthshire and Eastern Glamorgan- 

 shire, 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 Coalfield 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 Coalfield. 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 Cardiff Natural History 

 Society also, we have freely availed ourselves, acknowledgement of 

 all of which will be made in due course. 



In order that the map of the Coalfield should present tlie 

 structure as conspicuously as possible, it was necessary to subdivide 

 the great mass of Coal-measures which had been represented by 



