FOSSIL REEFS: PERMIC 433 



Fragments of limestone similarly consolidated occur, though more 

 rarely, on the sides of these knolls themselves. I would call these 

 reef-breccias." (Tiddeman-84:(5oi'.) The knolls are crammed 

 with brachiopods, pelecypods, crinoids, corals, etc., many fairly 

 perfect. This, however, is true only in a general sense, for in 

 places the limestone is apparently entirely devoid of fossils, though 

 this, as in the case of many of the other reefs cited, may be due 

 to obliteration of the organic structure. 



Marr (62) has pointed out the abundant evidence of folding 

 and thrusting in the rocks of this region, and he would explain 

 these knolls as due wholly to tectonic movements, the thickening 

 of the limestone being due to folding and thrusting. That the 

 region has been much disturbed is clearly evident from the facts 

 given by Marr, but that the knolls are wholly due to tectonic causes 

 seems doubtful. The original reefs of the limestones would serve 

 as centers of resistance in which the cumulative effects of the 

 thrusts would be most strongly marked. 



Fossil Reefs of Bryozoa and Other Organisms. 



Bryozoan Reefs of the German Zeciistein. In the Zech- 

 stein of the southeastern district of Thuringia in Germany reef 

 structure is well developed. The reef-forming organisms here are, 

 however, no longer corals but Bryozoa. These bryozoan reefs form 

 large block-like masses of structureless dolomite which lies scattered 

 within the normal bedded Zechstein strata. When erosion has 

 carved away the enclosing bedded strata, the reef mass stands out 

 in relief, forming frequently isolated bastion-like mounds, not un- 

 commonly surmounted by a castle or an ancient burg. The reef- 

 forming organisms are chiefly closely crowded masses of Acanth- 

 ocladid anccps, Fenestella retiformis, Phyllopora and other Bryo- 

 zoa. Corals are wholly absent, but brachiopods are well represented 

 by Productus horridns, Stroplialosia goldfiissi, Terehratula elon- 

 gata, and Spiriferina cristata, while the pelecypods are represented 

 by Pseudomonotis speiuncaria and Prospondylns liebeamus. The 

 most abundant organism, however, is a lime-secreting sponge or 

 hydrocoralline, Evinospongia, which covered the cliffs up to the 

 level of the sea. These reefs grew upon the cliffs of older rocks 

 which projected as islands and as lines of crags above the floor of 

 the early Zechstein sea. They extended along the southern bofrder 

 of the Harz old land and the East Thuringian peninsula, from 

 Kostritz past Possneck, where they are especially well developed, 



