508 Mr. AiKiN on the Wreh'in und on the 



Preen and Kenler. The texUirc of this stone is loose, so as readily 

 to admit the infiltration of water, in consequence of which the horn- 

 blende decomposes into a yellowish-brown clay, and then the rock 

 is apt to be confounded with clayey sandstone-slate. 



The space between the outburst of this bed and of the quartz-grit, 

 hereafter to be mentioned, is a valley, the bottom of which is occu- 

 pied by patches of a sandstone^ varying considerably in its external 

 appearance, presenting no marks of stratification or regular position, 

 and (as I apprehend) not belonging to the series of strata, but quite 

 superficial and composed of the materials of the two beds upon 

 which it is situated, together with small shells, either eiltire or in 

 fragments, belonging chiefly to the genus cardlum. It ahvays con- 

 tains mica, but for the most part in small scales, and dispersed irre- 

 gularly through its substance. 



- The quartz-grit^ which is the next bed, consists essentially of 

 quartz in rounded grains from the size of a pin's head to that of an 

 egg. In some parts it is so entirely free from admixture as to be 

 well fi.tted for the finer kinds of porcelain, since it acquires a snowy- 

 white colour by calcination ; but more generally it is mixed with an- 

 gular fragments of the bed which lies beneath it, in a state of greater 

 or less decomposition. Its northern boundary is the Arcal hill, the 

 eastern side and top of v/hich it entirely covers; it then skirts along the 

 eastern side of the Wrekin, overspreading it to about one third of its 

 height widi conical hillocks. It is interrupted by the valley of the 

 Severn, but re-appears on the south of this river, constituting the high 

 ridge v*"hereon are situated the parks of Acton-Burnwel, and Frodesley ; 

 it then runs parallel to the Lawley, but separated from it by a deep val- 

 ley; the ridge then rapidly declines in height, and applies itself on the 

 eastern side of Caer Caradcc (as it had before done on the Wrekin) 

 accompanying this hill along its whole length, and then terminating. 



