Miss M. M. Ogilvie — Coml iri the "Dolomites." 5 



giving rise to strange anomalies in the geological succession, which 

 could only be explained by regarding every case as one of con- 

 temporaneous deposition of different classes of rock very close to 

 one another, so-called " Heteropism." Such difficulties can only 

 be solved by stratigraphy, and to that we must turn for proof of 

 the data on which the Coral Reef theory rests. 



For the sake of clearness in writing, we prefer to use, instead of 

 the triple term applied to the reef-dolomito by Mojsisovics, the 

 single name given by von Richthofen, of " Schlern dolomite," ' from 

 its characteristic occurrence at Schlern Mountain, south of the 

 Groden Valley. 



II. — Normal Marine Formations of Mid-Trias in the Southern Alps — 

 Submarine Volcanic Action in Upper Fassa and the neighboui'ing 

 districts — The "Dolomite Reefs" of Enneberg and Ampezzo 

 correspond to part of the Normal Marine Deposits of the South. 



Whereas during the Wengen and Cassian period, volcanic activity 

 was rife in the northern part of the area covered by the sketch-map, 

 an accumulation of marine deposit appai'ently went on during a 

 steady subsidence of the sea-floor over the southern areas. Great 

 thicknesses of limestone and dolomite represent this period in the 

 southern part of the South Tyrol, and in the Venetian and Berga- 

 masker Alps. These are known in different localities as Esino 

 limestone, Marmolata limestone, Schlern dolomite. The fauna is 

 liable to great variation, but includes for the most part a typical 

 assemblage of Mollusca, Eohinoderms, Corals, and Gyroporellas (sea 

 algae). This we may regard as the normal oceanic formation of the 

 mid-Triassic period in the Southern Alps. 



In the Upper Fassa and Groden, Enneberg and Ampezzo districts, 

 intermittent outpourings of volcanic matter took place from one or 

 more submarine craters, associated perhaps with the proximity of this 

 part of the sea to pre-Triassic land of Paleozoic and crystalline 

 rocks, and with Triassic earth-movement. Be that as it may, the 

 southern rocks of Schlern dolomite, Marmolata and Esino limestones, 

 were clearly collected in deeper waters than the contemporaneous 

 deposits immediately to the north. This is nowhere better seen than 

 at Schlern Mountain, where the deep-sea deposits on the south side 

 of Schlern pass rapidly into the volcanic lavas and shallow-water 

 deposits, on the Seisser Alpe to the north. According to von 

 Richthofen's original interpretation of this district, the upper part 

 of the " Schlern dolomite " of Schlern was younger than any of the 

 sedimentary beds on the Seisser Alpe, a stratigraphical fact of 

 general import, which many geologists have since verified at this 

 point. 



Following an irregular line eastward and south-eastward, we 

 may trace the same occurrence of stratigraphical facies. It takes 

 place most suddenly where the Wengen lavas are thickest, i.e. in 

 Upper Fassa. The dovetailing of the dolomitic and calcareous 



1 Sclilem Dolomite. Vide von Eichthofen, " Geognostisclie Beschreibung der 

 Umgegend vou Predazzo, St. Cassian und der Seisser Alpe," 1860. 



