436 PRINCIPLES OF STRATIGRAPHY 



advocates of the reef theory to regard these deposits as more strictly 

 nullipore reefs, in which corals played only a secondary part. The 

 organisms of these massive dolomites have for the most part been 

 destroyed during the alteration of the deposit, but it has been possi- 

 ble to ascertain that the chief lime contributors were a coral, 

 Tliecosmilia suhdichotonia, and a coralline alga, Diplopora annu- 

 lata. The abundance of this and other calcareous algae is the cause 

 for the frequent interpretation of this mass as a nullipore reef. 

 Brachiopods {Koninckina leonhardi, RhyncJionclla faucensis) , pele- 

 cypods {Daonclla parthanensis) and cephalopods {Ptychites acutus, 

 Gymnites palinai, Japonitcs ganghoferi, Hungarites bavaricus, etc.) 

 occur at a few points, as for example, in the massif of the Zug- 

 spitze, but are as a rule very rare. Large gastropods (Chemnitzia) 

 occur at many localities in the reef masses. The bordering heter- 

 opic limestones sometimes consist largely of Diplopora fragments, 

 and as a rule are very rich in organic remains, especially close to 

 the reef. 



Recently the problem has been attacked by Professor Skeats 

 (82) from the chemical and petrographical side. He started with 

 the ascertained facts that in modern coral islands remote from land 

 areas and volcanic rocks the amount of insoluble residue in the reef 

 rock is negligible. The same is true also of many coral rocks asso- 

 ciated with volcanic rocks, though those in the proximity of the vol- 

 canic masses were found to contain a considerable quantity of in- 

 soluble material, amounting in some cases to 4 per cent, or over. 

 With this as a basis, he made numerous analyses of the dolomites, 

 which showed the prevailing purity of the rock, the percentage of 

 insoluble residue being in the majority of cases less than one per 

 cent., and frequently almost zero. Where residue is present, it can 

 generally be attributed to association wath contemporaneous vol- 

 canic rocks, as is the case in the raised coral reefs of Fiji. 



Taking the purity of the rock, the absence of structure and its 

 occurrence as enormously thick masses in the surrounding clastic 

 strata into consideration, there appears to be no other mode of ori- 

 gin than that due to the growth of corals, with an abundance of cal- 

 careous alg?e, foraminifera and echinoderms, such as are found in 

 some modern coral reefs. These Triassic reefs formed a barrier 

 reef to the land mass lying to the north, whose main axis consisted 

 of the crystalline rocks now forming the central chain of the Alps. 

 In the beginning of Triassic time continental sediments spread north 

 from these highlands, forming the Bunter Sandsteiri deposits of Ger- 

 many. In mid-Triassic time, however, a marine invasion from the 

 north caused the deposition of the jMuschelkalk, only to be fol- 



