were derived. I need hardly say that this injustice was unintentional, and arose from forgetfulness, chiefly the result of the circumstances under which the Memoir was composed. The documentary materials for it were collected from different persons at different times, and were reduced to order at intervals in different parts of England. Wales, and Ireland. Anything like research into books was almost necessarily precluded, and the attention was fixed on the materials which were at hand, and which could be carried about in the portmanteau.
This absence of research into the labours of previous or contemporaneous writers is a defect which it is difficult for those to avoid who are almost constantly engaged in field work and debarred from access to libraries, except at rare and short intervals. It has been indeed hitherto sufficiently difficult for the officers of the Geological Survey to find time to give any written account even of their own Labours, the results of which have been chiefly published in the form of maps and sections.
In the following Memoir the attention is confined solely to the facts observed in the district; from some questions that have been put to me, however. I believe that a few preliminary words respecting the relation of the Carboniferous rocks of South Staffordshire to those of the neighbouring districts will not be out of place.
I have been asked especially as to the reason of the absence of the groups of rock known as Millstone grit. Carboniferous limestone, and Old Red sandstone, between the Coal-measures and the Upper Silurian rocks of South Staffordshire.
If we proceed from the South Staffordshire to the North Staffordshire coal-field, a distance of only 20 or 25 miles, we find a vast difference in the constitution of the Carboniferous rocks. In South Staffordshire the Carboniferous rocks consist of Coal-measures only, the maximum thickness of which does not seem ever to have much exceeded 1,000 feet. In North Staffordshire these beds are far more numerous, and attain an aggregate thickness four or five times greater. Thick masses of sandstone occur about their base, which are grouped together under the name of the Millstone grit. Below this, as we go towards Derbyshire, we find thick beds of black shale, in some places
