526 OF THE PHYSICAL STRUCT UKE 



sess similar structural features with those of our Appalachian 

 chain. AVhile the older strata of the Berwyn mountains, as de- 

 scribed by Mr. Murchison (Silurian System), would seem, by 

 their altered character, and frequently inverted dips, to mark a 

 close proximity to one of the great lines of disturbance of the dis- 

 trict, that lying towards the northwest, from which has been prop- 

 agated a combined uplifting and tangential force ; the contom* of 

 the undulations, lying more towards the southeast, when unaf- 

 fected by faults or local disrupting action, exhibits a general con- 

 formity to our law of a steepening flexure, on the side towards 

 which the movement has proceeded. As illustrations of ihis law, 

 we would beg to refer the reader to a few of the beautiful sections 

 appended to Mr. Murchison's work on the Silurian System. 



First. Plate 31, fig. 5. Section across the Ludlow and Brecon 

 anticlinkl, exposing the valley of elevation of Wigmore lake. 



Second. Plate 34, fig. 3. This exhibits, to the northwest, the 

 lower Silurian on end, for some distance from its contact with 

 the Cambrian, after which it passes by a bold sigmoid flexure, 

 in which the southeast dips are very steep, beneath the upper 

 Silurian. 



Third. Plate 34, fig. 7. Shows, on the northwest, inverted 

 Jlexures or foldings, in the Llandeilo flags, then steep southeast 

 dipping Caradoc sandstone, and, following this, the Upper Silu- 

 rian and the Old red, with gi'adually diminishing dips. Fig. 8, 

 of the same plate, presents analogous phenomena, though they 

 are less distinct. 



Fourth. Plate 34, fig. 9. Displays an inverted and folded 

 flexure, succeeded by steep southeast dips, in the flagstones of the 

 Cambrian, following which are two normal arches in the lower 

 Silurian. 



To these Sections may be added the Vignette, page 359, pre- 

 senting an axis in the Cambrian rocks of Caermarthcnsliire. 



In the eastern portion of this district, bordering the Malvern 

 hills, the flexures would appear to be related, according to the 

 same law, to the great line of elevating action, extending in a 

 north and south direction through that region. The steeper sides 

 of the arches are now towards the ivest, and the lower rocks are 



