SILURIAN SYSTKM 167 



commonest: Lingula late, ll'ilmmin Wilsoni, Camarototchia nucula, 

 Leptcena lavigata, Chonetes striatella. At the top of these shales 

 there are gome beds of earthy flagstone which are quarried and are 

 known as the Leiotwardine flags ; they contain remains of starfish 

 (Lapworthura and Palccocoma\ large Orthoceras, and Arthropods of 

 the genera Pterygotus and Eurypterus, 



The Aymestry limestone is a bluish-grey earthy limestone of 

 varying thickness, and often split into several beds by intercalated 

 lands of shale. At Aymestry it is well exposed in the gorge of 

 the river Lugg and is said to be 175 feet thick. Ite commonest 

 fossils are Pentamerus Knighti, Lingula Leivisi, Wilsonia Wil- 

 soni, and Dayia navicula. The outcrops of the Ludlow Beds in the 

 typical district of Ludlow and Aymestry are shown in Fig. 56. 

 The total thickness of the series in Shropshire is about 2600 fi-.-t. 



In Staffordshire the Woolhope limestone reappears at Great 

 Barr, east of Walsall, the Wenlock Beds are well exposed at 

 Dudley and the higher beds at Sedgeley, the Silurian at all these 

 places being brought up in anticlinal flexures from which the over- 

 lying Carboniferous rocks have been removed by denudation. 



Downtonian. In Shropshire the Upper Ludlow shales 

 consist in the lower part of soft grey shales with thin bands of 

 limestone, and in the upper part of grey and green calcareous flags 

 at the top of which is a bed of greenish grey argillaceous sandstone 

 surmounted by greenish laminated sandstones, including a thin layer 

 consisting of the bones and spines of fish and large Crustacea ; this 

 layer is known as the " bone bed," and has been met with at many 

 localities. 



The bone bed is succeeded by the Downton sandstone, a fine- 

 grained and thin-bedded yellowish sandstone which is quarried 

 for building stone at Downton Castle near Ludlow, and contains 

 Lingula cornea, Pteraspis Banksi, Eurypterus lineatus, and other 

 Merostomata. This is about 50 feet thick, and is succeeded by 

 reddish flagstones and olive-green shales which yield Lingula cornea 

 with remains of fish and Crustacea. Above these are purple 

 sandstones without fossils. 



In a recent paper the Misses Elles and Slater 4 recognise the 

 following subdivisions, with a total thickness of 540 feet : 



Feet. 



Eurypterus shales . . . 120 

 Downton sandstone ... 50 

 Chonetes flags . . . .150 

 Rhynchonella flags . . .120 

 Dayia shales .... 100 



A similar series reappears in the Woolhope and Malvern districts 



