Chapter I. § 1. Introduction. It is my intention in the following communication to describe the principal phenomena exhibited by the great deposit of magnesian limestone which stretches on the eastern skirt of the central chain of our island, from the neighbourhood of Nottingham to the southern extremity of Northumberland. I had, in the year 1821, an opportunity of examining several portions of this deposit (especially in the county of Durham), and of verifying some interesting details connected with it which had appeared in the Transactions of the Society*. During a part of the two following summers I examined its whole western escarpment, and most of the localities which seemed likely to show its general relation, or to throw light on the structure of its subordinate parts. I venture to hope that a connected account of these observations, to which many additions have been made during subsequent visits to certain parts of the formation, may not be thought unworthy the attention of this Society. After the production of the rocks of the carboniferous order, the earth’s surface appears to have been acted on by powerful disturbing forces, which, not only in the British Isles, but through the greater part of the European basin, produced a series of formations of very great extent and complexity of structure. These deposits (known in our own country by the name of new red sandstone and red marl, and when considered on an extended scale, comprising all the formations between the coal-measures and the lias)