BY E. C. ANDREWS. 183 



the dissection of the eastern uplands was carried on from the 

 maturity of the previous cycle to a very slightly advanced stage 

 during the cycle of subsidence. The subsidence of the coast 

 gave diminished stream action along the lower portions of the 

 watercourses. River grade was also reached, no falls interrupting 

 the courses of the streams. 



The sinking of the maturely (or adolescently) developed coast 

 and shore of the previous cycle was the occasion of its investiture 

 by coral growths to form the Great Barrier Reef. These growths 

 kept pace with the gradual subsidence, and, as in other coral reef 

 regions, numerous deep water lanes became coexistent with the 

 growth of the Great Barrier, being determined probably in part 

 by tlie old watercourses of this area of drowned topography. 

 The evidence points to the limitation of luxuriantly growing 

 coral masses to the outer centre and edge of the shelf, owing to 

 the turbid water west of the centre of the shelf, the recession of 

 the shore line from the edge of the continental plateau permitting 

 of their existence in the clear water to seaward, while the turbid 

 water of the closer inshore area militates against its western 

 expansion. Exceptions occur in the deeper off-shore areas of 

 mountainous coasts possessing inconsiderable streams (coast 

 north of Cairns). The inner and central portions of the fairly 

 flat continental shelf seem determined by the conjoint influences 

 of tides and dominant currents in the way of redistributing the 

 loads brought down by the rivers, and the material lost to the 

 islands and mainland by the agencies of marine erosion. Gain 

 to this area is also represented by various animal and plant 

 growths containing calcareous tissues, coral growths being con- 

 fined to the formation of island fringing reefs. 



This cycle of coastal depression was interrupted in modern 

 times, as regards the shore,* by an epicycle of elevation, which 

 may have originated ni a shifting of the pivotal axis, inasmuch 

 as that, while apparent elevations along the coast line are con 



* The anticline to the west across which the canons of the coastal rivers 

 have sawn their way appears to have been in process of formation for a con- 

 siderable period. 



