THE OKDOVICIAN SYSTEM 



Bala and Caradoc Series. Continuing the above succession' 

 in the Shelve district the Bala Beds are well exposed in the Spy 

 Wood section. At the base are the Spy Wood grite and flags passing 

 up into shales ; these beds yield Trinuclem concentricus, Orthis 

 oilliijntiiinut, J'iplograptus truncatus, Climacograptus bicornis, and 

 other fossils. Above comes the Marrington Group, a set of grey 

 and black shales with interstratified beds of andesitic ashes and 

 breccias or agglomerates ; the highest shales are overlain uncon- 

 fonnnbly by the Silurian (Upper Llandovery Beds), the Hirnant 

 Beds not being exposed. 



Hope 

 Bowdler 



Ticffprton Norton 



Wenlock 

 E^dge 



S. 



Fig. 88. SECTION NEAR HOPE BOWDLER IN SHROPSHIRE (after E. 8. Cobbold). 



c. Wcnlock limestone. 

 ii. \\Vnlock shale, 

 it-. Llandovery Beds. 



I. Longville flags. 



.-. Chatwall sandstone. 



h. Harnage shale. 

 g. Hoar Edge grite. 





On the eastern side of the Longmynd the succession in the 

 Caradoc district was first worked out by Murchison and formed 

 the type of his "Caradoc sandstone." This was subsequently 

 proved to be only a local facies of the Bala Series. The succession 

 as corrected by Callaway and Lapworth is as follows : 



Llandovery Beds (unconformable) 



/ Trinudtus shales. 

 Caradoc I Acton shales and limestone, 

 sandstone, < Cheney Longville flags. 

 2000 feet I Harnage shales. 



\ Hoar Edge grits and sandy limestone. 



All these beds contain fossils, and the Acton Beds have yielded 

 Lichas laxatus, Ampyx, Orthis Actonioe, 0. flabellulum, and many 

 corals, so it is probable that they represent the Bala limestone. 

 The highest or Hirnant Beds are concealed by the overstep of the 

 Silurian. 



3. Cumberland and Westmoreland 



Ordovician rocks occupy a large area in the Lake District, 

 which was the scene of Professor Sedgwick's earliest work on tin- 



