4 Miss M. M. Ogilvie — Coral in the "Dolomites." 



Dachstein dolomite, well stratified and often of very great thickness, 

 builds the highest terraces and precipices. The Cassian, Wengen 

 and Buchenstein sedimentary beds are exposed on the passes between 

 " reefs," on their lower slopes, and over the large meadows 

 which the people of the place call" Alpen." The Muschelkalk and 

 Werfen series form the bed of the streams in the rapidly descend- 

 ing mountain valleys. It may be at once remarked that typical 

 fossils have been found in all members of the succession. In the 

 "reef-dolomite" fossil remains are extremely poor and scanty; 

 plant algae are got even more often than Corals, Gasteropods, or 

 Bivalves. Ammonites occur, but usually in too meagre a state of 

 preservation to be of much service in identifying the age of 

 the rock. 



Besides the layers of volcanic ash and lava which are interbedded 

 with the Wengen beds, there is every here and there a massive 

 looking volcanic rock, Augite Porphyry, which surprises the eye 

 by its strong contrast to the doloraitic rocks. Everyone knows that 

 Coral growth in our present seas is particularly luxuriant where 

 volcanic action is occasionally felt, and this seems a strong argument 

 in favour of the view which explains these Triassic dolomites as 

 Coral limestones, largely magnesic, which were built in a volcanic 

 sea of the far-away Trias period. The later conversion of such 

 magnesic limestone reefs into pure dolomite also finds its parallel 

 in recent reefs. So that the " Coral Eeef Theory of the Dolomites " 

 presents, as a theory, no problem which is not in harmony with 

 recognized facts, unless we except the enormous thickness attained 

 by the reefs, and the occurrence on their upper surfaces and slopes 

 of an appearance which Mojsisovics observed and called " overcast 

 bedding." 



A geological theory, however, stands by virtue, not of its 

 probability argued from Nature's Present, but its absolute fitness 

 to the facts observed in Nature's Past. And, when the same facts 

 may bear two or even more explanations, the theory which is to 

 stand in Science must fight for its position as the fittest survivor ! 

 "We have to ask ourselves if the Coral Reef theory offers the only 

 probable explanation of the dolomite cliffs. The mere occurrence of 

 a couple of thousand feet of limestone or dolomite is part of the 

 A B C of Geology, when taken as the accumulation of ordinary 

 marine deposit. Dachstein dolomite is such a rock, and it still 

 carries testimony of its origin in the numerous Megalodon bivalves 

 and other fossils which it contains. Again, a considerable amount 

 of variation in the thickness of any marine deposit might be expected, 

 especially where volcanic eruption had previously disturbed the sea- 

 floor and produced all degrees of inequalities by heaping up its 

 ashy flows in some parts more than in others. But the special 

 difficulty said to meet us in the case of the Cassian and Wengen 

 dolomite of South Tyrol is, that rocks of 2000 feet in thickness rise 

 quite suddenly from the midst of sedimentary earthy beds, and show 

 certain curious appearances in relation to them. The dolomite rock 

 seems to dovetail at its extremities into the marly and ashy beds, 



