BY E. C. ANDREWS. 821 



contrasted with the conditions obtaining simultaneously at Lady 

 Robinson's Beach. 



(/) The Hawkesbury River. — Visitors to Gosford will remember 

 that the train travels for nearly a mile and a half over a sand-flat 

 as Woy Woy is approached. It is raised a few feet only above 

 sea-level, is composed of sand, and contains many thousands of 

 shells in its upper portions exactly similar to those occurring in 

 the associated waters. The surface is not irregular like those 

 sand heaps piled up b}^ winds, or those formed by heavy waters 

 and winds as at Lady Robinson's Beach. There are also, in this 

 secluded spot, no waves competent to pile up sand-bars, nor 

 streams capable of forming deltas high above sea-level. 



When the oscillation of subsidence occurred which converted 

 the Lower Hawesbury and its branches into salt-water bays, the 

 loads of sand and silt still brought down from the Blue Mountains 

 and Goulburn River District by the floods were partly swept out 

 to sea along the main channel, and partly deposited by the lagging 

 current in the sheltered arms of the river. Debris also was 

 brought down from the neighbouring hills by the streams entering 

 from about Gosford and Woy Woy, and rearranged by the tides 

 to form wide shoals in the quieter spots, on which, as they 

 approached the surface, whole hosts of shells grew. A slight 

 movement of elevation then converted these shell-flats into dry 

 land habitable by man. 



A similar explanation accounts for the great flats skirting Lake 

 Macquarie, and crossed on their western margins by the Newcastle 

 trains. 



{g) Narraheen, Rock Lily, Dee Why and Curl Curl Lagoons. — 

 Plate xliv., supplied by Mr. M. Morrison, illustrates the general 

 appearance of this portion of the coast. To understand the 

 successive stages of growth, we must refer to the activities in 

 operation since the initiation of the canon cycle. The general 

 uplift which resulted in a warp for the Sydney area probably 

 submerged the old coast-line of the Lithgow plain, as is evidenced 



