INTRODUCTION 



5 



the structure of Shropshire ; for that county not only contains every sedimentary 

 formation from the lias to the slates inclusive, but is also rendered most complex by the 

 numberless dislocations of the strata, through the agency of volcanic rocks. The only 

 other modern writers who had touched upon the ancient rocks of this part of England, 

 were Mr. Leonard Horner in a memoir on the " Mineralogy of the Malvern Hills, " 

 Mr. Weaver in one on the " Geology of the Tortworth District," and Mr. J. Yates in a 

 short paper on " Parts of the central Counties." These essays which are included in the 

 Geological Transactions, though constituting valuable additions to our knowledge at 

 the periods of their publication, had reference to limited tracts only, in most of which 

 anomalous and disrupted relations prevented the adoption of any general view of a 

 succession of the strata, 



In this condition of the subject, I first explored the borders of England and Wales 

 in 1831. The order of succession seen in the ridges on the left bank of the Wye, 

 between Hay in Herefordshire and Builth in Brecknockshire, where the Old Red 

 Sandstone is distinctly underlaid by grey fossiliferous strata, first led me to suspect, 

 that I had met with a district containing a good part of the evidence required to lead 

 to a systematic study of our older formations j a surmise which was confirmed by fol- 

 lowing out these rocks upon their line of bearing to the neighbourhood of Ludlow and 

 Wenlock, where I found them much expanded. I explained my view of the subject 

 to the first meeting of the British Association, held at York, and afterwards to the 

 Geological Society of London. Perceiving, however, that a subject so new and so 

 large could not be really advanced, except through patient and repeated examination, 

 I re-explored the same districts, in 1832, and submitted details of the new acquisitions 

 to the Geological Society ; accompanying my memoirs with a set of geologically co- 

 loured maps of the Ordnance Survey. 



An effort to classify these deposits was then made ; but it was not until the close of 

 the summer of 1833, that I was enabled to publish a tolerably correct synopsis or table 

 of the various formations in the extensive region, over which my observations had 

 progressively extended. Seven years have since elapsed, during which my attention has 

 been almost exclusively given to the development of this subject and its collateral 

 branches. 



During the summer in which my first observations were made, Professor Sedgwick 

 commenced a general inquiry into the structure of North Wales, for which his previous 

 acquaintance with the slaty and crystalline rocks of Cumberland eminently qualified 

 him. He first endeavoured to connect the transition rocks of the age of Dudley with 

 certain calcareous slates pointed out by Mr. Greenough in North Wales ; but finding 

 no concordance between them, he was, to use his own expression, " driven to a new 

 base line," in other words, to work upwards from the central axis or oldest rocks of 

 Wales. As soon as he perceived that I had observed the links which connect the Old 

 Red Sandstone with some of the inferior masses of his region, he felt the importance of 



