Ch. XXVII.] 



LOWER WENLOCK. 

 Fisr. 637. 



559 



Fig. 636. 



Cabjmene Blumcnbacliii 



Brong. 



Wenlock, Ludlow, and 



Aymestry limestones. 



Fk 



SpTicerexochus minis, Beyrich, 

 coiled up. 

 Dudley ; also in Ohio, 

 M". America. 



Phaeops 'Asap7ius) caudatus, Brong. 

 Wenlock, Aymestry, and Ludlow rocks. 



tripartite division of the dorsal crust is almost lost (see fig. 639), is 

 very characteristic of this division of the Silurian series ; and there are 

 numerous other genera and species. 



Fig. 639. 



1 



Fig. 640. 

 "'^^^^^^^ 



Graptolithus Zudensis, Murchison. 

 Ludlow and Wenlock Shales. 



Bomalonotus delpJiinocephalus, Konig. 

 Dudley Castle. £ nat. size. 



Lower Wenlock. — a. Wenlock Shale. — This, observes Sir E. Mur- 

 chison, is infinitely the largest and most persistent member of the 

 Wenlock formation, for the limestone often thins out and disappears. 

 The shale, like the Lower Ludlow, often contains elliptical concretions 

 of impure earthy limestone. In the Malvern district it is a mass of 

 finely levigated argillaceous matter, attaining, according to Prof. 

 Phillips, a thickness of 640 feet, but is sometimes more than 1000 feet 

 thick in Wales, and is worked for flagstones and slates. The prevail- 

 ing fossils, besides corals and trilobites, and some crinoids, are several 

 small species of Orthis, Cardiola, and numerous thin-shelled species of 

 Orthoceratites. More than one species of Graptolite, a group of zoo- 

 phytes before alluded to as being confined to Silurian rocks, is very 



