292 Transactions. 



have resulted from coast-retrogradation normally taking place towards the 

 end of the stage of maturity in the " delta cycle with stationary crust,"* 

 a period that might possibly bo correlated with that at which a valley 

 lowland was developed in the Middle Clarence Valley.f Deep, dissecting 

 valleys, with broad terraces, some of them at a height of 300 ft., are the 

 work of erosion during the later discontinuous uplift, and here, as else- 

 where on this coast, the latest rejuvenation has been a very short period 

 in progress. 



The fore-set portion of the delta, which, however, does not show strati- 

 fication, may be examined in the banks of the river near the Clarence 

 Bridge. It consists of gravel of fairly even texture, few pebbles being 

 over 4 in. or 5 in. in diameter, but there is a considerable admixture of 

 finer gravel and sand, and some patches of sand. The material is fairly 

 well cemented. The fore-set portion is distinctly marked off from the top- 

 set (or at 'east from the subaerial top-set) beds by its bluish-grey colour, 

 corresponding to a low state of oxidation of the finer material, the latter 

 beds bein»' oxidized and of a yellow to reddish-yellow colour. The top- 

 set beds begin with a boulder-bed, possibly of subaqueous or beach origin, 

 which is followed by gravel and clay strata, and their average thickness 

 on the delta proper is about 80 ft. There are very thick accumulations 

 of oxidized fluviatile beds on some lower terraces, which may possibly 

 indicate downward oscillations interrupting the general upward movement. 



3. The Rock Platform near Flaxbourne. 



Well-preserved remnants of a wave-cut platform which indicate uplift 

 of several feet may be seen half a mile north of the mouth of the Flax- 

 bourne River. The rock exposed on the shore is a fine-grained, argillaceous 



C C 



Fig. 8. — Diagram illustrating the Theorem that the Amount of Uplift indi- 

 cated by Residuals of a Wave-cut Platform is less or greater than the 

 Height of the Residuals above their Base according as the Pre-uplift 

 Position of High-water Mark was Seaward or Shoreward of its Present 

 Position. 



sandstone overlying the Amuri limestone. It is in a vertical attitude, 

 but exhibits no bedding, and is but little jointed. Marine denudation 

 planes it off to a surface which slopes gently seaward, and which from a dis- 

 tance appears absolutely smooth, though closer inspection reveals numerous 

 inequalities with a relief of a few inches (see Plate XI), and the tabular 

 remnants of the slightly higher platform, several of which are shown in 

 the photograph, have an exactly similar surface and seaward slope. 



Their surface is several feet above the present level of high tide, and 

 they therefore indicate uplift. The height of the residuals above their bases 

 is 6 ft., but this cannot be taken as an absolute measure of the amount 

 of uplift unless it is assumed that the position of high-water mark (in plan) 

 was the same immediately before the uplift as it is now. 



* J. Barrell, Bull. Geol. Soo. Am., vol. 23 (1912), p. 396. 



t C. A. Cotton, "The Physiography of the Middle Clarence Valley," Geogr. Journ., 

 vol. 42 (1913), p. 228. 



