ZOOLOGICAL AND LITHOLOGICAL DISTINCTIONS OF THE COAL-FIELD. 475 



under Lyne, &c.) has been already proved by the discovery of Sir Philip Egerton, Bart., 

 who has found at Silver Hill near Madeley (see map) several species, including those 

 observed by myself in this district, associated with the same Uniones as in the Wol- 

 verhampton field. Again, several species of these Uniones are equally abundant in the 

 coal-field of Coal Brook Dale, where the discoveries of Mr. Prestwich prove that they 

 are also found in ironstone measures associated with the same fishes 1 . 



The marked differences in the mineral character of the measures of the north or Wol- 

 verhampton tract, as compared with those of the Dudley district, are not confined to 

 the beds of coal and ironstone ; for while in parts of the Dudley field, large masses of 

 sandstone form the base of the carboniferous series, such rocks are wholly wanting in 

 the northern tract, the strata of shale and ironstone being at once incumbent upon 

 Silurian rocks. 



1 I have little doubt that, when well examined, all the coal-fields of England will be found to contain the 

 characteristic species of the Scottish and other coal-fields already published byAgassiz. Mr. Bowman of Gres- 

 ford called my attention some time ago to the fact of the prevalence of Megalichthys and other fishes in the 

 Denbighshire coal-field. 



In referring my readers to the instructive shaft sections in the following pages, I 

 cannot avoid noticing the obligations I owe to several gentlemen connected with this 

 coal-field. To the names of Mr. Downing, Mr. Best, Mr. J. Barker, and Mr. Dawson 

 already mentioned, I must add those of Mr. W. Mathews of Green Hill, Mr. Bennett 

 of Dudley, and Lieutenant Eaton, R.N., to all of whom I am indebted for much obliging 

 assistance. 



