8o rROCEEDlNGS OF THE GEOLOGICAL SOCIETY. 



examine witli some care the so-called "pre-Cambrian" rocks of Wales. 

 So much has been written regarding these rocks, and so keen a con- 

 test has been waged over them, that a mere allusion to them, still 

 more a decided statement of opinion regarding them, may possibly 

 serve to revive the turmoil ; for amid so wide a diversity of view one 

 can hardly venture to express agreement with any one observer 

 without seeming to place one's self in formal opposition to all the 

 rest. I shall try to avoid anything approaching to the nature of 

 controversy, and state as plainly as I can the results to which my 

 own observations have led me. While it would be out of place 

 here to offer even a brief summary of the voluminous literature 

 which during the last twenty years has been devoted to the discus- 

 sion of this subject, I shall take advantage of the opportunity which 

 the present Address affords me to state where I think the work of 

 the Geological Survey among these rocks has received important 

 corrections from that of subsequent observers. 



At the outset I wish to express my hearty admiration of the 

 labours of my predecessors in the Survey of Wales. When we con- 

 sider the condition of geology, and especially of petrography, at the 

 time when these labours were carried on, when we remember the 

 imperfection of much of the topography on the old one-inch maps 

 (which were the only maps then available), when we call to mind 

 the rugged and lofty nature of the ground where some of the most 

 complicated geological structures are enclosed, we must admit that 

 at the period when these maps and sections were produced they 

 could not have been better done ; nay, that as in some important 

 respects they were distinctly in advance of their time, their publi- 

 cation marked an era in the progress of structural geology. The 

 separation of lavas and tuffs over hundreds of square miles in a 

 mountainous region, the discrimination of intrusive sheets and erup- 

 tive bosses, the determination of successive stratigraphical zones of 

 volcanic activity among some of the oldest fossiliferous formations, 

 were achievements which will ever place the names of Eamsay, 

 Selwyn, Jukes, and their associates high in the bede-roll of British 

 Geology. ISTo one ever thinks now of making a geological excursion 

 into Wales without carrying with him the sheets of the Geological- 

 Survey map. These form his guide and handbook, and furnish him 

 with the basis of information from which he starts in his own 

 researches. 



But science does not stand still. The most perfect geological map 

 that can be made to-day will be capable of improvement thirty or 



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