44 The Rev. W. D. Conybeare on the probable 



heulandite. The formula which seems best to express the 

 constitution of levyne is 



N. >S + 3AS 3 + 5 Aq, which differs from that usually adopted 

 P J for chabasite in containing one atom less of silica, and 

 one atom less of water. 



VII. On the probable future Extension of the Coal-fields at 

 present worked in England. By the Rev, W. D. Cony- 

 beare, M.A. 9 F.R.S., §c. 



[Continued from vol. iv. p. 348.] 



I" HAVE already pursued my proposed examination through 

 *■ a considerable proportion of the coal-fields of our central 

 district (namely, the eastern division, including the fields of 

 Ashby-de-la-Zouch and Warwickshire, and the smaller patches 

 near Ashborne on the south of the great Derbyshire chain). 

 I consider the general result to be, that throughout this cen- 

 tral district the whole stratification is so extremely disturbed 

 and undulating that we are scarcely able to form any antici- 

 pations as to the probable prolongation of the beds which 

 can be at all relied upon ; but that in very few instances the 

 boundaries of the fields have as yet been ascertained with any- 

 thing like scientific exactness ; that a survey undertaken ex- 

 pressly with a view to this inquiry is undoubtedly very de- 

 sirable ; and that it is little to the credit of a nation like ours, 

 so peculiarly dependent on this branch of her mineral re- 

 sources, that we thus continue contentedly to acquiesce in a 

 state of ignorance so easily removed. We here see a strong 

 instance of our want of a regular school of mining, such as is 

 possessed by many other countries. 



In continuing my own imperfect hints with a view to such 

 ulterior inquiries, I shall first complete the central districts by 

 noticing the Dudley coal-field. 



Dudley Field. — The boundaries of this field can hardly yet 

 be considered as accurately ascertained. The anticlinal ridge 

 of transition limestone of Dudley throws up the beds which crop 

 out all round it; and as on the eastern edge of the field near Wal- 

 sall, the same transition limestone again emerges, we may con- 

 sider the coal-measures around Bilston as lying in a trough be- 

 tween these points. I do not find any account of the exact limits 

 of this trough on the N.W. border from the Dudley lime- 

 stone range to Cannock, at the northern apex, or on the N.E. 

 from Cannock to Walsall ; but I rather believe that the beds 



