MACKIE — OX THE BOTTOM-KOCKS. IS'-^ 



as the slates of Llanberris and Bangor were derived, have long since 

 subsided beneath the waves. 



Passing the Meuai Straits, towards the west flanks of the moun- 

 tainous range of Snowdon, we find " huge buttresses of very ancient 

 grit, schist, slate, and sandstone," of Cambrian date. 



But, after all, the best British example of lowest sedimentary or 

 ^' bottom-rocks " occurs at the Longmynd mountains, in the typical 

 region of " Siluria," Shropshire. And there and at Bray Head only 

 (with one or two isolated exceptions, referred to subsequently) have 

 any traces of fossils as yet been found. 



I remember, many years since, seeing the Longmynds, when I knew 

 - very little about Geology, and nothing at all of the history of those 

 hills, and thinking, as I passed them, w^hat old hills they looked. The 

 late Professor Edward Forbes and others have expressed the same 

 feeling ; and certainly there is something very remarkable in their 

 appearance. The valley to the west of them is bounded by some low 

 hills of micaceous schist, ranging along the base of a craggy ridge of 

 trap mountains, of which the Wrekin forms the northern extremity, 

 and continued on the south side of the Severn by those of Acton- 

 Burnell, Frodesley, the Lawley , Caer Caradoc, and Hope-Bowdler. These, 

 like the Wrekin, have the longest diameter from north-east to south- 

 west, and rise very abruptly, at an angle of 60°, from the plain below. 

 The vale in which Church Stretton is situated separates the trap moun- 

 tains from the remarkable mass of hills called the Longmynds, which 

 gradually rise to the height of 800 feet, and then with a level and 

 nearly unvarj'ing summit stretch for several miles towards Bishop's 

 Castle. A peculiar squareness seems to characterize these mountains, 

 and from Stretton Vale, whence three or four series of hills are seen 

 rising one above another, this feature is particularly apparent. The 

 individual mountains are generally separated from each other by a 

 narrow deep glen, traversed in its length by a small stream, sometimes 

 foaming in cascades over ragged ridges, and sometimes more gently 

 flowing beneath overhanging woods. The Longmynds for the most 

 part are covered with heath and a short grass that furnishes exten- 

 sive pasturage for numerous flocks of sheep ; and from their flanks 

 brooks and streamlets break out and flow northward into the plain 



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