434 



PRINCIPLES OF STRATIGRAPHY 



past Saalfeld to Eisenach and southward around the peninsula to 

 Liebenstein. The floor of the Zechstein sea had previously been 

 covered with the black Kupferschiefer mud rich in decaying organic 

 matter, chiefly the carcasses of dead fish and decomposing algae, and 

 in which the copper now obtained from it was precipitated. These 

 deposits did not cover the ledges upon which the reefs subsequently 

 grew when normal marine conditions were established. These reefs 

 grew to the height of 40 to 100 meters, with steep sides which, how- 

 ever, often show the interfingering with the clastic limestone which 

 surrounds their flanks. This limestone is often almost devoid of 

 organic remains, forming a dark "Stinkstein" or a blue compact 



Fig. gi. Dolomite reefs of South Tyrol. Richthofen reef on left with tongue- 

 like extensions into the contemporaneous marls. Sett Sass on 

 right. C D — Structureless Schlern-dolomite. (Kayser.) 



lime, both well stratified, and succeeded by a porous dolomitic 

 "Rauchwacke." The growth of the reefs came to an end with the 

 closing of the outlet from the open ocean to this epicontinental sea, 

 and the beginning of gypsum and salt deposition (referred to in 

 the preceding chapter), the reefs being eventually buried under 

 hydrogenic or clastic deposits. 



The Triassic Reefs of the Tyrol. The dolomites of the 

 southern Tyrol are regarded by many geologists as examples of 

 fossil reefs on a gigantic scale. They consist of huge, structure- 

 less and more or less circumscribed masses of limestoiie or dolo- 

 mite representing a distinct facies of the mid-Triassic, which is 

 elsewhere represented by the bedded and often highly fossiliferous 

 Cassian, and underlying Wengen and Buchensteiner divisions of the 



