180 STUDIES FOR STUDENTS 



from the growing corals of the rim come to rest below wave-base. 



Such a breccia, at the foot of reefs of Mississippian limestones in 



Great Britian, has been described by Tiddeman. 1 



The characteristics of coral breccia may be enumerated: 



i. Like all wave and tide breccias, coral breccia is either a 



rubble or a pudding breccia. Crackle and mosiac breccias are not 



to be expected. 



2. The matrix consists of the fine detritus of the reef. 



3. Both matrix and fragments are singularly devoid of siliceous 

 and argillaceous impurities. An exception occurs in reefs which 

 receive more or less waste from an adjacent land. 



4. Reef-rock breccia may show little or no trace of bedding. 

 In the core of the deep boring of the Funafuti atoll, which passes 

 through this rock to a depth of 1,114 f ee t, the only stratification 

 found was that due to such irregular accumulation of detrital 

 material as occurs between and around the corals. 2 The numerous 

 Silurian reefs of Wisconsin and Iowa show little or no trace of 

 bedding from top to bottom, while areas occur within them of con- 

 glomeratic or brecciated structure. 3 In the case of the wave-driven 

 fragments of the island rock some sorting and bedding with low dips 

 are to be expected, and the talus formed below the reef probably 

 shows rude layers dipping outward at the angle of repose. 



5. The fragments of coral breccia show varying amounts of 

 wear. Least worn are fragments of reef rock accumulated below 

 wave-base. The island rock necessarily approaches a conglomerate 

 in the rounding of its constitutent masses. How short a time and 

 distance are needed to destroy the angularity of fragments is seen 

 in a photograph and description by Kent 4 of the result of a single 

 tropical hurricane of a few hours' duration in 1884. A fringing 

 reef was wrecked and its fragments, swept inland, were piled above 

 reach of the highest tides. Massive head-corals were torn up and 

 rolled together like the small pebbles of the beach and ground down 

 to subspherical symmetry. 



1 R. H. Tiddeman, Rept. British Soc. (Newcastle-on-Tyne) , p. 602. 



2 Judd, quoted by Sollas, op. cit., p. 128. 



3T. C. Chamberlin, Geology of Wisconsin, I, 184; W. H. Norton, Iowa Geol. 

 Surv., IX, 424; XI, 307. 



4 Saville Kent, Great Barrier Reef of Australia, pp. 50-52. 



