344 A. ^V. GRABAU — PALE0Z(3IC CORAL REEFS 



with a wedging out of marginal rims of the reef between the sedimentar}^ 

 beds. 



DEVONIC AND CARBONIC REEFS OF BELGIUM 



Dupont* has described the reefs in the Devonic limestones of Belgium. 

 The reefs have at first impression the appearance of amorphous lime- 

 stone, passing into more or less saccharoidal rock. On weathered faces 

 a somewhat brecciated structure appears, together wdth numerous out- 

 lines of corals or sponges, slightly put in relief by a granular lime 

 which is more soluble. The mass consists of a vast number of skeletons 

 of coelenterates which have been profoundl)^ altered, as evidenced b}^ 

 microscopic examination. It is generally impossible to separate the 

 lamina of these masses with the hammer, but in a few^ cases where per- 

 fect separation has been possible the true character of the remains was 

 determined. They are chiefly stromatoporoids, which make up a large 

 part of the reef, though other organisms are not uncommon. 



The stromatoporoids show their characteristic structure only on weath- 

 ered surfaces, while on fresh fracture the rock is compact, often with 

 glassy fracture, and full of cavities, and without any evidence of organic 

 remains. Ko stratification is visible in this mass, but is w^ell marked 

 in the flanking beds of clastic limestone. Beside the stromatoporoids 

 (Stromataclis and Pachystroma) the reef formers include Favosites, Al- 

 veolites, and more rarely Cyathophylloids ; but Cyathophyllum csespitosum 

 occurs on the margin of some reefs in crowded heads of 1.50 to 2 meters 

 in diameter. 



The Carbonic " Calcaire de Waulsert" is described b}^ Dupontfas 

 composed of an agglomeration of Stromataclis bulbaceous and Ptylostroma 

 fibrosa. To the surfaces of these adhere numerous fronds of Fenestella. 

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

 coralloides and a few other rare t3^pes. Small massive heaps or islets of 

 these reefs are scattered through the formation. Around the reefs, and 

 entangled with them, occur limestones of diverse character, but chiefly 

 marked by the clearness of their stratification. Among these limestones 

 we can distinguish two distinct varieties, the crinoidal and the amor- 

 phous. The crinoidal rock, formed by the dissociation of the joints of 

 crinoid columns, occurs in channels in the reefs. 



Summary of Characters of Paleozoic Coral Reefs 

 We may sum up the characters of the reefs mentioned as follows : In 



*E. Duponl: Sur I'origine des calcaires devoniens de la Belgique ; Bulletin de I'Acadt'mie 

 Royale de Belgique, ser. 3, T. 2, 1881, pp. 264-280. 



•f E. Dupont: Sur les origines du calcaire carbonif^re de la Belgique; Bulletin de TAcad^mie 

 Royale de Belgique, ser. 3, T. 5, 1883, pp. 211-229. 



