ch. xxvlt.] 



WENLOCK FORMATION. 



557 



2. WenlocJc Formation. 



We next conic to tlie Wenlock formation, which has been divided 

 (see Table, p. 550) into the Upper Wenlock, or Wenlock Limestone, 

 and the Lower Wenlock, including, first, the Wenlock shale, and sec- 

 ondly, the Woolhope limestone and Denbighshire grits. 



Upper Wenlock. — Wenlock Limestone. — This limestone, otherwise 

 well known to collectors by the name of the Dudley limestone, forms a 

 continuous ridge in Shropshire, ranging for about twenty miles from 

 S. W. to X.E., about a mile distant from the nearly parallel escarpment 

 of the Aymestry limestone. This ridgy prominence is due to the 

 solidity of the rock, and to the softness of the shales above and below it. 

 Near Wenlock it consists of thick masses of gray sub'crystallirie lime- 

 stone, replete with corals and encrinites. It is essentially of a con- 

 cretionary nature ; and the concretions, termed " ball-stones " in Shrop- 

 shire, are often enormous, even 80 feet in diameter. They are of pure 

 carbonate of lime, the surrounding rock beino- more or less arc-ilia- 

 ceous.* Sometimes in the Malvern Hills this limestone, according to 

 Professor Phillips, is oolitic. 



Among the corals in which this formation is so rich, the " chain- 

 coral," Holy sites catenulai'ius, or Catenipora escharoides (fig. 631), may 



EalysiUs catenularius, Linn, 

 sp. Syn. Catenipora escha- 

 roides, Goldf. Upper and 

 Lower Silurian. 



Fig. 



Favosites Gothlandica, Lam. 

 Dudley. 



a. Portion of a large mass ; less 

 than the natural size. 



b. Magnified portion, to show 

 the pores and the partitions 

 in the tubes. 



Tig. 63 



Omphyma turbinatum, 

 Linn. sp. Cyathophyl- 

 him, Goldf. 



Wenlock Limestone, 

 Shropshire. 



be pointed out as one very easily recognized, and widely spread in 

 Europe, ranging through all parts of the Silurian group, from the Ay- 

 mestry limestone to near the bottom of the series. Another coral, 

 the Favosites Gothlandica (fig. 632), is also met with in profusion in 

 large hemispherical masses, which break up into prismatic fragments, 



* Murchison's Siluria, chap. vi. 



