Physical Geography. 9 1 



turn to the Shropshire area between Church Stretton 

 and Chirbury, including the Cambrian rocks of the 

 Longmynd, this is what we find. On the vertical and 

 highly inclined strata of the Cambrian and Lower 

 Silurian rocks, the conglomerates and limestones of the 

 Upper Llandovery beds form in the lower country a kind 

 of narrow fringe, surrounding great part of the area, and 

 lying from 500 to 900 feet lower than the broad, flat- 

 topped, and gently undulating hills of the Longmynd 

 and Shelve. Almost on the highest level of one of 

 these flats, at the well known Bog-mine, there is a 

 small outlying patch of Upper Llandovery beds, formed 

 of hard quartzose sandstone, at a height of 1,150 feet 

 above the sea, as roughly indicated in the following 



diagram. 



FIG. 21. 



1. Cambrian grits, &c. 



2. Lingula flags. 



3. Tremadoc and Llandeilo beds. 



4. Pentamerus beds. 



5. Wenlock shale. 



The inference is obvious, that these Pentamerus- 

 bearing strata began to be deposited at the bases of the 

 hills, and that by degrees, during a process of slow 

 submersion, the sea crept on and on inland, accompanied 

 by the deposition of marginal Upper Llandovery beds, 

 till at length, like an island in the coral seas of the 

 Pacific (but without the corals), this old Silurian Isle 

 was entirely swallowed up and buried, deep beneath 

 the succeeding great accumulations of Upper Silurian 

 strata, which in the adjoining area of Wenlock and 



