16 
before.” I will bo excused from the imputation of attempted 
self-laudation when I state, that that district was completed 
principally by Sir Henry de la Beche and Mr. Logan before 
my connexion with the survey began. 
I shall give one other example of the application of geolo- 
gical principles to the solving of a question which will one 
day be of great economic importance : it is drawn from the 
work of the geological survey now in progress in the centre 
of England. As our sections in that country are still incom- 
plete, I can only at present explain the principles on which 
our conclusions depend by means of diagramatic sections. 
Underneath the true new red sandstone on the borders 
of Nottinghamshire and Derbyshire, is a strip of country noticed 
by Smith, but first fully described by Professor Sedgwick. He 
divided its rocks into magnesian limestone, and lower new red 
sandstone.* These rest unconformably on the coal measures, 
which they follow in the order of superposition. Owing to dif- 
ferences in lithological character, and the absence of the lime- 
stone, the Staffordshire, Warwickshire, and Shropshire coal-fields 
were for long considered as unsurrounded by these beds. The 
upper new red sandstone was supposed to rest directly on the 
coal measures. By degrees, however, their existence in sundry 
places w x as noticed or surmised, and now on some of the smaller 
published maps indications of their existence may be found, 
both where they are, and where they are not. With a differ- 
ence they are so exceedingly like the new red sandstone, that 
they have for the most part been confounded with it, at least 
by almost all those engaged in the working of mines ; and 
again, in some respects their mineral character here and there 
strongly resembles certain red portions of the coal measures. 
They are, therefore, in most maps sometimes incorrectly deli- 
neated, but distinguished from, — and sometimes erroneously 
included in, the coal measures, or new red sandstone, as the 
case may be. 
It chanced, however, last year, that by dint of constant 
* The Pontefract rock, of Smith, 
