Ch. XXV.] 



MOUNTAIN" LIMESTONE. 



403 



CARBONIFEROUS OR MOUNTAIN LIMESTONE. 



It has been already stated (p. 359), that this formation underlies the 

 Coal-Measures in the South of England and Wales, whereas in the North 

 and in Scotland marine limestones alternate with Coal-Measures, or with 

 shales and sandstones, sometimes containing seams of Coal. In its most 

 calcareous form the Mountain Limestone is destitute of land-plants, and 

 is loaded with marine remains, — the greater part, indeed, of the rock 

 being made up bodily of corals and crinoids. 



The Corals deserve especial notice, as the cup-shaped kinds, which 

 have the most massive and stony skeletons, display peculiarities of struc- 

 ture by which they may be distinguished, as MM. Milne Edwards and 

 Haime first pointed out, from all species found in strata newer than the 

 Permian. There is, in short, an ancient or Paleozoic, and a modern or 

 Neozoic type, if, by the latter term, we designate (as proposed by Prof. 

 E. Forbes) all strata from the triassic to the most modern, inclusive. The 

 accompanying diagrams (figs. 514, 515) may illustrate these types ; and, 

 although it may not always be easy for any but a practised naturalist to 



Fig. 514 



Paleozoic type of lamelliferous cup-shaped Coral. Order Zoantharia kctgosa, Milne Edwards 

 and Jules Haime. 



a. Vertical section of Gampophyttum flexuo&um (Cyatho- 

 phyllum, Goldfuss); £ nat. size: from the Devonian of 

 the Eifel. The lamellae, are seen around the inside of the 

 cup ; the walls consist of cellular tissue : and large trans- 

 verse plates, called tabula;, divide the interior into cham- 

 bers. 



b. Arrangement of the lamellm in Polycmlia profunda, Ger- 

 mar, sp. ; nat. size : from the Magnesian Limestone, Dur- 

 ham. This diagram shows the quadripartite arrangement 

 of the lamellae characteristic of paleozoic corals, there being 

 four principal and eight intermediate lamellae, the whole 

 number in this type being always a multiple of four. 



C. Stauria astrmceformis, Milne Edwards. Young group, 

 nat. size. Upper Silurian, Gothland. The lamellae in 

 each cup are divided by four prominent ridges into four 

 groups. 



Fig. 515. 



Neozoic type of lamelliferous cup-shaped Coral. Order Zoanthaeia apokosa, M. Edwards and 



J. Haime. 



a. Parasmilia centralis, Mantell, sp. Vertical section, nat. size. 

 Upper Chalk, Gravesend. In this type the lamellm are mas- 

 sive, aud extend to the axis of loose cellular tissue, without 

 any transverse plates like those in fig. 514 a. 



b. Cyathina Bowerbankii, Edwards and Haime. Transverse 

 section, enlarged. Gault, Folkstone. In this coral the lamellm 

 are a multiple of six. The twelve principal plates reach the 

 central axis or columella, and between each pair there are 

 three secondary plates, in all forty-eight. The short interme- 

 diate plates which proceed from the columella are not counted. 

 They are called pali. 



c. Fungia patellars, Lamk. Recent : very young state. Dia- 

 gram of its six principal and six intermediate septa, magnified. 

 The sextuple arrangement Is always more manifest in the 

 young than in the adult state. 



recognize the points of structure here described, 'every geologist should 

 understand them, as the reality of the distinction is of no small theoreti- 

 cal interest. 



