17 
practice and study in the field, my colleague, Mr. Hull, dis- 
covered a key to the separation of these rocks from any others 
of the district ; and the progress of the mapping of the country 
has shown, that everywhere, except in accidental cases, they rest 
unconformably on the coal measures, and that the new red 
sandstone is unconformable on both. 
Now, for reasons that I cannot at present enter upon, it is 
known to geologists that concealed treasures of coal probably 
underlie the larger portion of the great area of new red sandstone 
that surrounds the coal-fields of central England. Already in 
great part of South Staffordshire most of the best beds of 
ironstone are being rapidly exhausted ; and in great part of the 
district “ the thick coal ” has been extracted, or the workings 
are so drowned by water, in consequence of the faults being 
worked through by gate-roads, that its drainage is next to 
impossible. The day will surely come when this and other 
coal-fields will be worked out ; and the question will then arise, 
at what depths beneath the unconformable covering that shrouds 
them, will coal-bearing strata be found in various localities? 
This is an important problem, which the work we are now 
engaged upon will go far to solve. 
By means of numerous observations of the dip of strata, and 
the construction of sections on a true scale, it is often possible 
to determine the thickness of any special mass of rocks. Within 
a given area, where, therefore, is the new red sandstone likely to 
have the smallest thickness ? or, in other words, where can we 
predict that the concealed coal measures rise nearest to the 
surface ? 
In this diagram you will observe that the lower new red sand- 
stone, or Permian strata, rise against the coal-fields on the east 
and west, and that the whole is overlaid by the upper new red 
sandstone.* It is therefore to be expected, that in this district, 
the lower new red sandstone strata intervene between the upper 
new red sandstone and coal measures throughout. This sus- 
picion is confirmed by the circumstance, that within the new 
* Illustrated by a diagram of the disposition of the strata round the South 
Staffordshire and Coalbrook Dale Coal-fields. 
5. 
B 
