FOSSIL REEFS: DEVONIC . 423 



corals of less importance as reef builders also occur. Brachiopods 

 and molluscs appear to be rare, however. A remarkable feature of 

 this reef is the enclosing rock, which is a calcilutyte and wholly 

 unfossiliferous so far as exposed, except in the upper layers. Or- 

 ganisms seem to have been confined entirely to the reef, while the 

 surrounding area was the site of the deposition of the finest lime 

 mud. It is highly probable that the fineness of this mud explains 

 the absence of macroscopic forms of life, because few animals can 

 exist in muddy water such as this must have been. 



Elsewhere in this horizon reef structures of similar type are 

 developed. They are well shown in the Lewistown limestone of 

 central Pennsylvania, where, near Tyrone, they consist almost wholly 

 of stromatoporoids of the same species as at Anderdon, together 

 with the Favosites, Cladopora and Diplophyllum found there. In 

 the Manlius limestone of New York State similar Stromatopora 

 reefs are found. These are more especially of the bedded type, 

 consisting of one or more layers of Stromatopora heads of various 

 sizes and belonging to a number of genera and species. Other or- 

 ganisms are rare, and the enclosing strata are mostly calcilutytes. 



It is a common fact that such bedded Stromatopora reefs are 

 enclosed in calcilutytes, and this seems to be due in part to the 

 absence of other organisms which could furnish lime sand. The 

 mutual attrition of the massive Stromatopora heads seems to have 

 resulted chiefly in the formation of lime mud. If so, the progress 

 of sedimentation here must have been an exceedingly slow one. 



Dev^onic Coral Reefs. The Devonic formations abound in 

 coral reefs both in North America and Europe. They occur in the 

 lower Devonic of Konjepruss, Bohemia, in the Onondaga of New 

 York, and the Falls of Ohio, the Traverse group of Michigan, the 

 Devonic of Canada, of Belgium, the Eifel and elsewhere. The 

 details of the reef structure of only a few of these have been inves- 

 tigated, and these will be discussed at some length. 



Lozvcr Devonic Reefs of Konjepruss, BoJieniia. As exposed in 

 the quarries near Konjepruss, the lower Devonic limestone of Bo- 

 hemia (Fo of Barrande) shows a massive, structureless reef facies, 

 in which the zoogenic limestone is largely composed of massive 

 Favosites and stromatoporoids, while brachiopods, molluscs, trilo- 

 bites and small corals also abound, especially on the margin of the 

 reef. Laterally this reef limestone merges into a stratified, coralline 

 limestone (see Kayser and Holzapfel-55). The reefs are under- 

 lain by the Upper Siluric platey limestones and black graptolite 

 shales, but whether they rest directly on these deposits or are 

 preceded by shell layers has not been ascertained. 



