430 



PRINCIPLES OF STRATIGRAPHY 



tation-covered islets, such as are characteristic of coral reefs to-day. 

 Devonic Reefs of the Attaivapishkat River, Canada. In the 

 southern part of the Province of Keewatin, in Canada, reef struc- 

 tures occur in the Devonic limestones. (Bell-12 li-^G, 28G.) These 

 have been exposed in natural sections by the Attawapishkat River, 

 an affluent of James Bay. These reefs have the character of great 

 spongy and cavernous limestone masses often occupying the full 

 height of the cliffs, which is about 40 feet. They are structureless 

 masses of rudely lens-like character and "largely made up of fos- 

 sils, although the number of species does not appear to be great." 

 The principal forms are brachiopods (Meristella, Stropheodonta), 

 a trilobite and corals. Stromatoporoids are probably also among 

 the abundant reef-builders. The thinly bedded limestones which 

 enclose the reefs dip away from them at various angles, and are 

 sparingly fossiliferous. These beds are more easily removed by 







FiG. 8g. Reef mounds enclosed in bedded 

 formations of Devonic age. Atta- 

 wapislikat River, Canada. (After Bell.) 



Fig. 90. A single reef mass 

 left by erosion of the 

 bedded rocks. Attawa- 

 pishkat River, Canada. 

 (After Bell.) 



erosion, with the result that the reef masses stand out in bold relief 

 like the Klintar of Gotland. The numerous islets in the Attawap- 

 ishkat River "appear to consist of single masses," each of these 

 reef-cores being left in reHef by the removal of the surrounding 

 strata. They are locally known as z^^ngwanis by the native Indians. 

 (Figs. 89, 90.) 



Middle Devonic Reefs of the Eifel and Belgium. The Middle 

 Devonic Stringocephalus beds of the Eifel show in many sections 

 a typical reef structure similar to that already described for the 

 Devonic of North America. As in other cases, the reef masses 

 stand out in relief, forming high cliffs of structureless limestone 

 often dolomitized. The structure and topography are in many 

 cases modified by the eruption through these limestones of Tertiary 

 volcanic rocks. The chief reef-building organisms in these de- 

 posits are Favosites, Cyathophyllum, Endophyllum, Stromatopora 

 and Actinostroma. Brachiopods, gastropods, pelecypods and ceph- 

 alopods are also characteristic and sometimes abundant. The usual 



