UPPER SILURIAN ROCKS OF MONTGOMERY, NEWTOWN, AND WELCH POOL. 301 



the elevated trough, in the centre of which lies the Old Red Sandstone of the forest of 

 Clun. Though the junction of these rocks with the Old Red Sandstone is clearly de- 

 fined, it is not practicable to trace through these mountains the same subdivisions of 

 the strata as in the Ludlow district, there being no good representative of the Aymestry 

 Limestone, nor a trace of its beautiful fossils. Receding from the limits of the Upper 

 Ludlow Rock, we see in numberless well-defined and open sections a succession of infe- 

 rior strata, which conduct us downwards to well-marked Lower Ludlow Rocks, without 

 the intervention of a single bed of limestone, however impure. We occasionally meet, 

 however, with a narrow band, filled with the Terebratula Navicula, which may be con- 

 sidered to represent the Aymestry Limestone. 



Some of the harder beds of the Lower Ludlow are quarried for flagstones in Kerry 

 Hill and at Yechad, where they contain two species of Cardiola and numerous Grapto- 

 lites, fossils already described as characteristic of this subdivision, but which have never 

 yet been observed in the Upper Ludlow Rock. The same beds are quite as clearly 

 exhibited on the eastern side of Clun Forest, in the lower parts of the Black Hill, &c. 

 (The greenstone of the inhabitants.) We can thus clearly define both the Upper and 

 Lower Ludlow Rocks in that portion of the tract in which they pass upwards into the 

 Old Red Sandstone. 



Ludlow rocks, containing the same fossils, occupy nearly all the higher parts of the Long Moun- 

 tain (1330 feet) between the Corndon and the Breiddens, though the Upper Ludlow Rock is ill 

 developed. (See PI. 32. f. 2.) Below that zone, which is marked by the flagstones containing 

 the CardiolcE, is a badly defined succession of strata, for owing to the absence of any representative 

 of the Wenlock limestone it is impracticable to separate the strata underlying the flagstones from 

 those above them, and to decide, that this portion of shale belongs to the Ludlow, that to the Wenlock 

 formation. We are here, therefore, compelled to include both formations under the comprehensive 

 term of Upper Silurian Rocks; and the same absence of limestone and fossils obliges us to apply this 

 broad classification to large tracts in North and South Wales. 



The whole of the strata in the valley of the Severn from Newtown to the Breiddens are of this 

 age. They surround the town of Montgomery, and extend in undulating masses from Newtown to 

 Llanfair, and are admirably exhibited in the valley of the Berriew. They form all the ridges of the 

 beautiful upper park of Powis Castle, and are admirably laid open in the hill of Yr-Alt, N.N.E. of 

 Welch Pool. They are also repeated in troughs at Meifod, between the valleys of the Severn and 

 the Ffyrnwy l , these troughs being bounded by ridges of the inferior Caradoc sandstone. (PI. 32. f. 9.) 

 The Upper Ludlow is wanting throughout the greater part of this range, and the prevailing rocks 

 have the incoherent character of the Lower Ludlow and Wenlock shales. As the strata of these 

 hills are thrown over with reversed dips, they can be examined in numberless sections. The 

 whole of the Long Mountain is a trough-shaped elevation, the flagstones and lower shales rising 

 on all sides towards the flanks of the mountain. (PI. 32. f. 2.) On the western slopes, near Nelly 

 Andrew's Green and Gaithley, the lower argillaceous strata being near the volcanic range of the 



1 The English reader may be informed that the Welsh name of this river, Ffyrnwy, though apparently so 

 unpronounceable, has the agreeable and mellifluous sound of vernew. 



2 p 



