191G] on The Search for New Coal-Fields in England 031 



concealed coal-field,* and the result has been to show that the eastern 

 limit lies not far east of the valley of the Trent. Though not so 

 large as appeared possible to the Commission of 1905, this extension 

 is a notable addition to the visible coal-field, but its productiveness is 

 still a matter of doubt. Observations on the thickness of coal-seams 

 are difficult in boreholes, but so far the results have been disquieting. 

 The Denbighshire concealed coal-field offers a different problem. 

 Here it is not so much the existence as the accessibility of the 

 coal-seams which is in question, and the reason is found in a great 

 development of upper coal measures, mostly of a red colour and 

 barren of good coal, above the productive measures. The section 

 (Fig. 3) has been drawn from the escarpment of carboniferous Ume- 



Rocks 



1000 EOOO 3000 4000 Feet 



VERTrCAL SCALE. THREE TIMES THE HORIZONTAL 



Fig. 3. 



stone near Llangollen across the coal-field into Shropshire. It will 

 be noticed that the measures dip at a much steeper angle than in 

 Nottinghamshire, and that they are repeatedly thrown up and down 

 by faults. Both the angle of dip and the faults have been proved in 

 colliery workings as far east as the part marked " proved " extends. 

 Beyond that point the section is hypothetical. 



In the proved part a not uncommon relationship between the dip 

 and the faults is observable. The steep dip, if not counteracted, 

 would speedily carry the coal-seams to an inaccessible depth ; but the 

 tendency of the rather complicated faults is to bring them back to 

 their level. As a consequence the main seam keeps at a depth of less 

 than 2,000 feet for two miles or more. 



* An account of the investigation as a whole appears in " The Concealed 

 Coal-field of Yorkshire and Nottinghamshire " {Mem. Geol. Survey), 1913. 



