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



south of the Fassa-Groden barrier, extended also considerably west- 

 ward ; it was a basin in which, during Permo-Triassic time, volcanic 

 activity was never long absent. 



Comparing now the conditions existing in the West Indies 

 at present, the resemblance is most striking. We read from 

 Langenbeck ^ that barrier-reefs " have built on the outermost edge 

 of extensive banks of sediment which have been heaped up along the 

 whole North Coast of Cuba by sea-currents " (loc. cit. p. 18) ; and. 

 again, " It is exactly this difference in the degree of subsidence 

 which produces the contrasts (so very characteristic of the north- 

 west part of the Caribbean Sea) between great oceanic depths and 

 relatively shallow portions of the sea, the two abutting almost 

 directly on one another, united by steep slopes" (loc. cit. p. 24). 

 In the Australasian Archipelago we find essentially similar physical 

 and natural phenomena — in the Philippine Islands, the Solomon, 

 Pelew, and Fiji Islands, etc. There too, reef-Corals show special 

 favour for submarine ridges and plateaux in the immediate proximity 

 of areas of strongly-marked subsidence, and very generally where 

 volcanic agencies have recently been, or still are, active. Everyone 

 conversant with the literature of recent Coral-reefs will recall abun- 

 dant testimony of the co-operation of the same great geophysical 

 forces which influenced the Triassic seas of South Tyrol, and made 

 them locally suitable for the existence of beds of reef-Coral and the 

 development of a rich fauna. 



Guppy and other observers have stated that during " negative," 

 or shallowing movement, Corals grew seldom in reef-like fashion; 

 they tended rather to spread laterally and form extensive banks, or 

 even terraces. This is admirably illustrated by the Coral-banks 

 of the Raibl period. Their mode of occui'rence reminds one, 

 too, of the "Coral Oolite" beds of Jurassic deposits. The Coral 

 rock formed in South Tyrol in Eaibl time is not Limestone ; it 

 is a member of a highly Dolomitic series and is itself Dolomitic. It 

 must be remembered that the Dolomitism of the Raibl-Dachstein 

 period is by no means confined to South Tyrol, but is a common 

 feature in greater or less degree in the Alps and in Keuper deposits 

 elsewhere. The volcanic eruptions of Predazzo and Monzoni have 

 been attributed to the early part of the Raibl period. This would 

 conform with the local oscillations of level in neighbouring areas 

 and the temporary " back-flow " of the water. The Pelew and Fiji 

 Islands and the Sandwich Islands yield again good cases of analogy. 



Darwin's theory demands fairly constant equipoise throughout a 

 long geological age between the rate of growth of reef-Coral and 

 the rate of subsidence of the reef-basis. There is not satisfactory 

 evidence in favour of this in South Tyrol ; my special survey in a 

 part of the district seems to me to justify, without doubt, the 

 position of those authorities who have contended that the immense 

 thicknesses of " Schlern Dolomite " rock were an ordinary marine 

 deposit and not " Coral-reefs." 



1 Dr. E. Langenbeck, " Die Theorieen liber die Entstebung der Koralleninseln 

 und Korailenriffe und ilire Bedeutung fiir geopbysische Frageu." Leipzig, 1890. 



