Ridges, Troughs, &c. in the Strata, described. 165 



greatly on the S, and the Limestone to become surprisingly 

 changed to the southward, in its thickness and quahties, so as to 

 be with great ditficaltv recognised, when it appears again 44 m. 

 SE, in Balan Bank, south of the Severn, and whence, as I have 

 been informed, this Limestone Rock, in a thin and very bad state, 

 ranges \V of Woolaston and Westbr.ry, N of Minsterley, NE of 

 Haberley and Puherbach, SW of Leebotwood*, Sec. and that a 

 hne of small Coal-works (whose names were mentioned to me) 

 accompanies, throughout, this last range of bad Limestone, on 

 its NE side. 



The very irregular form and range of the Limestone which has 

 been mentioned above, seems to arise principally, from the nu- 

 merous inequalities or ridges and troughs on the surface of the 

 coarse Slate, on which it was deposited, partly from the subse- 

 quent dislocatrons occasioned by the Faults, and partly from the 

 still later and stupendous denudation, which the whole country 

 has suffered ; and bv the combined operations of which three 

 causes, numerous detaclied lengthened Basins or Troughs, and 

 patches of the Limestone are left, as memoriiJs of their opera- 

 tions. 



One of these detached Limestone Troughs i>early crosses 

 Anglesea, from Malldraeth Sands to Red-wharf, and has a small 

 Coal-field in and upon it, see Phil. Mag. vol. xliii. p. 325. 

 Another such Trough ranges along the south-we5,tern part of the 

 Menai straight. On the WSW of Caergwrle there are two de- 

 tached patches of Limestone laid bare, having Coal-measures 

 surrounding them, as I have been informed, and tiiat the most 

 eastern and largest of these denudations (which I have not seen, 

 but wherein Nant-v-Fritli Limowurks are situated) nearly re- 

 sembles that of Ashover, in many particulars. 



At Gwerclas on the SW of Corwen, part of a small Basin of 

 the same Limestone is seen, from under the alluvia whicii con- 

 ceals the greater part of it, as well as the vestiges of the super- 

 incimil)eiit Coal-measures, which the trials on the common NE, 

 are s;fid to have ascertained r On the W of Guilsfield I have 

 ascertained a narrow Trough of the bad Limestone ranging NE 

 and SW, in w hich some of the lower and barren Coal-measures 

 are found: and througli the W end of Welch-Pool Town, Powis- 

 park,and perhaps thence to Montgomery, there ranges the eastern 

 edge of another such Trough of the bad slaty and conglomerate 

 Limestone. Whether parts of similar Troughs of this same Rock 



* It lias licrt) said, that alioiit I* rn XE of Cliurcli-Stietton, it makfts a 

 sudden wlipcl to tlio N l'>, and ranges tiius, towards tl)e wtbtcni side c/' tlie 

 Wrckin Hill, with a N'W dip?. 



L 3 appear 



