282 THE CANADIAN NATURALIST, [Vol. vi. 



latter. Following up this investigation in 1832, he established 

 the great Merioneth anticlinal, which brings up the lower rocks 

 on the south-east side of Snowdon, and is the key to the struc- 

 ture of North Wales. From these, as a base, he constructed a 

 section along the line already indicated, over Great Arenig to the 

 Bala limestone, the whole forming an ascending series of enorm- 

 ous thickness. This limestone in the Berwyn hills is overlaid by 

 many thousand feet of strata as we proceed eastward along the 

 line of section, until at length the eastern dip of the strata is 

 exchanged for a westward one, thus giving to the Berwyn chain, 

 like that of Snowdon, a synclinal structure. As a consequence of 

 this, the limestone of Bala re-appears on the eastern side of the 

 Berwyus, underlaid as before by a descending series of slates and 

 porphyries. These results, with sections, were brought before 

 the British Association for the Advancement of Science at its 

 meeting at Oxford, in 1832, but only a brief and imperfect ac- 

 count of the communication of Sedgwick on this occasion appears 

 in the Proceedings of the Association. He did not at this time 

 give any distinctive name to the series of rocks in question. 

 [L E. & D. Philos. Mag. [1854] IV, viii, 495.] 



Meanwhile, in the same year, 1831, Murchison began the 

 examination of the rocks on the river Wye, along the southern 

 border of Radnorshire. In the next four years he extended his 

 researches through this and the adjoining counties of Hereford 

 and Salop, distinguishing in this region four separate geological 

 formations, each characterized by peculiar fossils. These forma- 

 tions were moreover traced by him to the south-westward across 

 the counties of Brecon and Caermarthen ; thus forming a belt of 

 fossiliferous rocks stretching from near Shrewsbury to the mouth 

 of the river Towey, a distance of about 100 miles along the 

 north-west border of the great Old Bed sandstone formation, as 

 it was then called, of the west of England. 



The results of his labors among the rocks of this region for the 

 first three years were set forth by Murchison in two papers pre- 

 sented by him to the Geological Society of London in January, 

 1834. [Proc. Geol. Soc. II., 11.] The formations were then 

 named as follows in descending order: 1. Ludlow, 2. Wenlock, 

 constituting together an upper group ; 3. Caradoc, 4. Llandeilo 

 (or Builth) forming a lower group. The Llandeilo formation, 

 according to him, was underlaid by what he called the Longmynd 

 and Gwastaden rocks. The non-fossiliferous strata of the Long- 



