250 The Founders of Geology LECT. 



formation, greywacke was believed to extend over all the 

 rest of the Principality. Let me quote a few sentences in 

 which Murchison describes his first entry into the domain 

 with which his fame is now so inseparably linked. " Tra- 

 velling from Brecon to Builth by the Herefordshire road, 

 the gorge in which the "Wye flows first developed what I 

 had not till then seen. Low terrace-shaped ridges of grey 

 rock, dipping slightly to the south-east, appeared on the 

 opposite bank of the Wye, and seemed to rise quite con- 

 formably from beneath the Old Eed Sandstone of Hereford- 

 shire. Boating across the river at Cavansham Ferry, I 

 rushed up to these ridges, and, to my inexpressible joy, 

 found them replete with Transition fossils, afterwards 

 identified with those at Ludlow. Here then was a key, 

 and if I could only follow this out on the strike of the 

 beds to the north-east, the case would be good." * 



With unerring instinct Murchison had realized that if 

 the story of old Greywacke was ever to be told, a begin- 

 ning must be made from some known and recognizable 

 horizon. It would have been well-nigh useless to dive 

 into the heart of the Transition hills and try to work out 

 their complicated structure, for even if a sequence could 

 then have been determined, there would have been no 

 means of connecting it with the already ascertained strati- 

 graphical series, unless it could be followed outwards to 

 the Old Eed Sandstone. But by commencing at the 

 known base of that series, every stage conquered was at 

 once a definite platform added to what had already been 

 established. 



The explorer kept along the track of the rocks for 



1 Life, vol. i. p. 182. 



