214 CHARACTERISTIC ORGANIC REMAINS OF THE WENLOCK FORMATION. 



seeing the width over which it has extended, must exceed seven hundred feet ; so 

 that we shall not exaggerate in assuming a thickness of one thousand feet for the whole 

 formation. 



Minerals. — The simple minerals hitherto observed in the Wenlock limestone of Shropshire, con- 

 sist of crystallized carbonate of lime in many forms, sulphate of barytes (rare), sulphurets of lead 1 

 and iron, peroxide of manganese in small quantities, crystals of copper pyrites (sulphurets), and 

 bitumen. The copper pyrites and bitumen are found in veins associated with white calcareous spar 

 lining the interior cavities, joints and fissures. When I first examined them at Lincoln Hill, I 

 thought they might, like many other metallic veins, communicate downwards with fissures, con- 

 nected with deeply-seated subterranean agency. Subsequent examination of some of these veins 

 exposed in the quarries of Bradeley Field, near Wenlock, has, however, convinced me, that many 

 of them are veins of segregation, which were formed when the calcareous matter was consolidating 

 and assuming its present concretionary structure. 



The limestone at Bradeley is crystalline, dark-coloured, and where not interfered with by hail- 

 stones arranged in thick beds having a slight inclination. When deeply cut into, short veins are 

 exposed, which are clearly seen to terminate both above and below. These are filled with white 

 calcareous spar, penetrated by separate crystals of copper pyrites. Other larger and vertical rents 

 have their walls lined with crystals of calcareous spar, the surfaces of which are coated over with 

 black bitumen. Upon opening the cavities with the pickaxe, this bitumen exudes, and flows over 

 the adjoining limestone. It was also stated by the workmen that large discharges of water accom- 

 panied the laying open of some of these cavities. Although such veins are particularly described 

 at this locality, they are also found in other places where the limestone is thick and crystalline, and 

 are invariably most abundant in the proximity of large unstratified concretionary masses. As they 

 never occur in the upper or lower small nodular beds, and can in some instances be observed, fairly 

 terminating at both ends in the limestone, it may be inferred that these veins are contemporaneous 

 with the rock in which they occur, in other words, that they have been formed at the time when the 

 purer calcareous matter separated from the argillaceous mass and formed the larger concretions. 



Organic Remains. — The most striking zoological distinction of the deposit consists in 

 the vast number of Corals with which it is charged. Among the most prevalent we 

 may enumerate Heliopora pyriformis (de Blainville) ; Catenipora escharoides (Lamarck) ; 

 Stromatopora concentrica (Goldfuss) ; Favosites Gothlandica (Lamarck) ; Cyathophyllum 

 turbinatum (Goldfuss); Limaria clathrata (Steininger) , &c. These corals, with many 

 others belonging to this and the other formations of the Silurian System, are figured in 

 PL 15 and 16., and will be described in a subsequent chapter by Mr. Lonsdale. The 

 Crinoidea, which are also very abundant, appear in PL 17 and 18 9 . 



The conchifers and mollusks of the limestone are figured in PL 12. Of these the 

 most common are Euomphalus discors, E. rugosus, and E. funatus, figs. 18, 19, and 20.; 

 Productus euglyphus and P. depressus, tigs. J and 2. ; Atrypa tenuistriata and A. aspera, 



1 It is said that there were formerly lead mines in this limestone near Much Wenlock, but they have been 

 disused for many years. 



2 The plates in which the corals and crinoidea appear not being completed while these pages are passing 

 through the press, I am unable to refer my readers to the figures. 



