628 Mr. Aubrey Strahan [March 17, 



possible extensions of the Midland coal-fields, while in Kent explora- 

 tions carried on during the last thirty years have revealed the existence 

 of a coal-field of not less than 170 square miles in extent, exclusive 

 of the part which lies below the sea. 



On the same map the regions where formations older than coal 

 measures have been found to lie below the Secondary rocks are indi- 

 cated by a lighter tint of grey. These regions, therefore, belong to the 

 same category as the areas left white, and need no further considera- 

 tion as possible sites of concealed coal-fields. It is to be noticed 

 that the white ruling borders the Kent coal-field on its western and 

 northern sides, and that it extends thence under London in a general 

 north-westerly direction through Buckinghamshire, Oxfordshire, and 

 Xorthamptonshire, towards Warwickshire and Leicestershire. The 

 existence of this barren tract has been proved by a number of 

 borings in and near London and in the counties named, but its 

 limits have not been ascertained. On its north-eastern side rocks 

 older than coal measures have been proved at Culford, Lowestoft, 

 and Harwich, rendering the existence of coal measures under central 

 and eastern Suffolk improbable, but there still remains unexplored 

 a tract extending north-westward through Essex, Bedfordshire, and 

 Rutland. On its south-western side there lies a great area of 

 unexplored ground. The south coast from Folkestone to Devon- 

 shire, and adjacent areas in Sussex, Hampshire, and Dorset, with 

 parts of Devonshire, Somerset, and Wiltshire, are unproved in the 

 sense that no boring has yet reached the base of the Secondary rocks. 

 What these rocks rest upon it is impossible to say, but their thickness 

 is likely to be great near the south coast. 



Time will not permit me to describe in detail the explorations in 

 all the concealed coal-fields. I propose, therefore, to select three 

 examples in order to illustrate the nature of the problems which arise 

 in the investigation. The purpose will be served by considering the 

 concealed coal-fields of Nottinghamshire with Yorkshire, Denbighshire, 

 and Kent. 



The Nottinghamshire coal-field is illustrated by a section (Fig. 2) 

 drawn from near Crich, in Derbyshire, to Kelham, near Newark-on- 

 Trent. Commencing in the Carboniferous Limestone, the line of 

 section crosses the visible coal-field in a distance of about 6|- miles. 

 Thus far it is founded on observations made at the surface on the 

 outcrop of the strata, the order in which they succeed one another, 

 and the angle of their dip. But it then enters a region in which 

 Permian (magnesian) limestone, Bunter sandstone, Keuper sandstone, 

 and Keuper marl in succession form the surface of the ground. These 

 formations lie unconformably upon the coal measures ; they are 

 inclined at a gentler angle, and have not been affected by the folds 

 which have bent the coal measures into syncliues and anticlines. It 

 follows that the newer strata are not parallel to the older, and may 

 rest upon any part of the coal measures, or even upon any older 



