Upper Silurian Rocks. 



93 



races, but beyond that into South Wales the limestones 

 disappear, or are occasionally only very feebly repre- 

 sented, and the whole consists chiefly of shales, some- 

 times sandy, in which no definite lines of subdivision 

 for the subformations can be drawn. 



FIG. 22. 



1. Caradoc sandstone (Lower Silurian'). 



2. Upper Llandovery limestone and sandstone^ 



lying unconformably on No. 1. 



3. Wenlock shale. 



4. Wenlock limestone. 



5. Lower Ludlow shales, concretionary. U PP er Silurian. 



6. Aymestry limestone. 



7. Upper Ludlow sandy flags and shales. 



8. Passage beds, and 



9. Old Red Sandstone. 



Far east of this, at Usk, Woolhope, May Hill, the 

 Malvern and Abberley Hills, and at Dudley and Walsall, 

 the limestone formations (so-called) are well developed, 

 while in North Wales the Upper Silurian rocks chiefly 

 consist of shales and interstratified grits without any 

 bands of limestone. Near Llangollen, where the shaly 

 strata are much affected by cleavage, they become true 

 slate. In Scotland, the Upper Silurian rocks occur 

 between the Solvvay Firth and the Cheviot Hills, and 

 are said to lie unconformably on the Lower Silurian 

 strata. Further north they only occupy small areas 

 near Lesmahago, and at the north-west base of the 

 Pentland Hills. 



All of these formations are in general terms 

 fossiliferous. The Wenlock limestone is in great part 



