432 PRINCIPLES OF STRATIGRAPHY 



Mississippic Reefs of Belgium. In the Mississippic (Tour- 

 nasieii and Viseen) of Belgium occurs a distinct reef facies known 

 as "Calcaire de Waulsort" and belonging in part to both of the 

 above subdivisions. This limestone is a massive, structureless ag- 

 glomeration of the stromatoporoids Stromatocus bulbaceus Dupont 

 and Ptylostroma fibrosa Dupont. To the surfaces of these hydro- 

 corallines adhere numerous fronds of the bryozoan Fenestella. 

 Corals play only a small part in these reefs, including Amplexus 

 coralloides and a few other rare types. The reefs are in the form 

 of small massive heaps or islets scattered through the bedded lime- 

 stones which surround them and are marginally entangled with 

 them. These limestones are of diverse character, and chiefly 

 marked by the clearness of their stratification. Two varieties of 

 this limestone may be distinguished, the amorphous and the crin- 

 oidal. The latter, formed from the dissociated joints of crinoid 

 columns, commonly fill the channels in the reef mass proper. As in 

 the case of the Devonic reefs, these also are disposed in the form 

 of fringing reefs parallel to the old shore, and separated from it 

 by a lagoon canal of greater or less width. In one case the reef 

 has been followed for a distance of 60 kilometers. 



Mississippic Reefs of Great Britain. In the Mountain limestone 

 of Great Britain certain structures occur which have been inter- 

 preted by Tiddeman (84; 85) as reefs, but this interpretation was 

 challenged by Marr (62). The structures in question occur in 

 the Craven district of Yorkshire, on the south side of the Craven 

 fault system, in the Pendleside and Clitheroe limestones. "The 

 form and the system of arrangement of the white limestones [of 

 the knolls] are peculiar. The stratification of the deposits is usu- 

 ally somewhat obscure, and the masses rise in the form of conical 

 or ovoid eminences up to a height of 300 or 400 feet. The change 

 of thickness occurs in a very limited horizontal extent. These 

 eminences ordinarily present upon their sides strata which dip 

 away from the mass in all directions ; but when the rocks of the 

 eminences have been quarried, or denuded by atmospheric agents, 

 one sees that the stratification, rough as it is, preserves its hori- 

 zontality or agrees with the direction of inclination of the sur- 

 rounding country. . . ." (Tiddeman-85 :ji'/ ; Marr's transla- 

 tion-62.) 



"At the foot of these mounds, or reef knolls, as I would call 

 them, we have in many places a breccia formed of fragments of 

 the limestone, which, I take it, have been broken off the reef above 

 between wind and water, and have subsequently been covered up 

 by the mud of the Bowland shales and compacted into a breccia. 



