180 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



In no case has Thurman or Gressly observed ancient coral reefs of very 

 great thickness (one hundred meters) at all to be compared with the 

 thickness claimed for modern reefs by Darwin and Dana (two thousand 

 feet). 



The evidence brought forward from the existence of recent lime- 

 stone beds of great thickness in Java and in the Philippines and other I 

 localities, to which reference has been made as proof of the great thick- ! 

 ness of coral reefs, must be taken as subject to modification. One i 



of the most interesting of the fossil coral reefs is the atoll of Ben- ! 



i 

 guet, in the island of Luzon, mentioned by Drasche. 1 It has walls of i 



five to six hundred feet above the valley, which itself is about four j» 



thousand feet above the sea level. The surface of the limestone is filled 



with red earth, often several feet in thickness. The limestones, unlike 



coral reefs, are distinctly stratified. The corals and other fossils belong 



to genera which still occur in the Indian Ocean of to-day, so that the 



limestones of the atoll of Benguet and of Northern Luzon belong to the 



most recent formations of the island, and from their description differ 



greatly from the coral reef limestones of to-day. 



Kichthofen's 2 theory that the Schlern Dolomite was a coral reef was 

 adopted in the main by Mojsisovics, 8 and their view r s, although opposed 

 by Gilmbel, 4 have received general recognition until comparatively re- 

 cently. Miss M. M. Ogilvie, in the Geological Magazine for January and 

 February, 1894, perhaps first called attention to the peculiar occurrence 

 of the so called coral reefs in the Dolomites. 



In the interesting account of coral in the Dolomites of South Tyrol 

 by Miss Ogilvie an entirely new view is taken of the reef-like appear- 

 ance assumed by the dolomitic massifs, which she traces to the move- 

 ment of the rocks in Tertiary times, and to the variation in the character 

 of contemporaneous Triassic deposits, her conclusions being that, "as 

 far as positive evidence goes, the coral rocks of South Tyrol in the 

 Wengen and Cassian period are not the majestic massifs of Dolomite, 

 but much less obtrusive lenticular masses of limestone," the " Cipit 

 limestones." 5 Miss Ogilvie has shown in the diagrams I. -IV., on Plate 

 II., (a) that coralline "Cipit limestone" and coral Dolomite form com- 



1 Drasche, R. von. Fragmente zu einer Geologie der lnsel Luzon. Wien, 1878. 



2 Geognost. Beschreib. der Umgegend von Predazzo in Siid-Tirol. 1860. 



3 Die Dolomit Riffe v. Siid-Tirol u. Venetien. 1879. 



4 Sitzb. d. Akad. d. Wiss. Munchen. 1873. 



5 See Plate II., February number of the Geological Magazine for 1894, and the 

 figure on page 53 of the same number. 



