BY E. C. ANDREWS. 177 



111 a mere advance-note like the present the proper discussion of 

 the above observations would occupy too much space, but briefly 

 their philosophy appears to me to be much as follows : — 



The coincidence of Barrier Reef and present coastal contours 

 points to an occupation by coral growths of a former coast line, 

 but the continuance in width of the shelf southwards of the limits 

 of reefs (coralline), and the great shoals thereon, points to a minor 

 part only of the shelf being formed of coral growths. 



It would appear that the almost uniform and smooth bottom 

 of the outer centre and eastern portions of the continental plateau, 

 combined with the great depths from which the Barrier rises, 

 argues a long period of marine erosion preceding the present 

 cycle* during which a uniform coast and smooth off-shore bottom 

 had been formed. The sinking of this uniform area allowed the 

 sea to trespass far over the old coast sands into the ranges, and 

 the corals — formerly prevented from forming barrier reefs, b}'' 

 reason of the practical coincidence of continental shelf margin and 

 shore line, and the excessively turbid character of the water on the 

 narrow fringe of the continental shelf — proceeded in the clear 

 waters of the shelf margin, now removed far seaward, to invest the 

 whole width of the smooth ofF-shore deposits with their masses, 

 and establish themselves as the Barrier Reef. 



Some connection probably exists between the present Reef 

 passages (and parallel channels) and the old watercourses of the 

 coastal area. 



The association of numerous rugged mountainous islands on the 

 inner centre of the shelf (and close in shore) and smooth shallow 

 interinsular seabottom, combined with traces only of coastal nips, 

 is suggestive of gradual subsidence with concomitant sedimenta- 

 tion rather than a period of equilibrium succeeding subsiden(^e 

 which would result in the formation of cliffs. f Magnificent 



* Cycle — the time involved in a movement of considerable extent or in the 

 development of a submarine plain or peneplain. 



t The existence of bar-bound rivers has, however, to be taken into con- 

 sideration. ^-^ - J ■>^ 



12 ^<^^C><2 





