On iJie Botany Watershed. 75 



The Botany watershed covers a superficial area of 5473 acres. 

 Of this surface, about 4562 are sand hills, and the remaining 

 913 acres are valleys of sand covered by bog — the whole over- 

 lying the solid sandstone rock which forms a large natural basin 

 from east to west, with a declivity from north to south towards 

 the sea at Botany. It would appear that the sand which covers 

 this watershed has been carried by the southerly winds from 

 the seashore near Botany Bay, and deposited in this basin. The 

 sand is perfectly free from loam or other viscid or clammy matter, 

 and is therefore highly absorbent. I may mention, that on 

 more than one occasion, I have filled a measure with five parts 

 of sand, and pressed down tightly so as to bring the sand even 

 with the top of the measure. Then I poured into the sand 

 which the measure contained, very nearly three parts of water. 

 After standing some short time, the sand so wetted settled down 

 about one-eighth of an inch below the rim of the measure, and 

 some of the water I had poured in, which had before been 

 covered with sand, appeared on the top of the sand about one- 

 sixteenth of an inch in depth. Of course, after the particles of 

 sand have been brought closely in contact by the application of 

 water, the absorbing power is sligthly decreased, still if sand be 

 tolerably dry it will always absorb considerably more than one- 

 half its own bulk of water. During my operations in this 

 watershed I have repeatedly had occasion to make borings to 

 ascertain the depth of bog, sand, and rock below the surface, 

 and I have found almost invariably, that the boring tools shortly 

 before reaching the rock have to pass through a stratum of 

 what appeared to be a yqyj tough, tenacious clay, which, during 

 the operation of boring, becomes mixed with sand, and which 

 mixture sticks so hard upon the tools as to materially impede 

 the boring, and prevent the withdrawal of the tools from the 

 holes. The highest swamp in this basin is called the Lachlan 

 Eeserve, the northern or head waters of which are led by 

 gravitation through Busby's Tunnel to Hyde Park in the heart 

 of the city. The sill of this tunnel is about 105 feet above the 

 level of the sea at Botany. The fall of the stream in the first 

 mile below the tunnel is 36 feet ; that of the second mile is 26 

 feet ; that of the third mile is 22 feet ; that of the fourth is 12 

 feet, and that of the last half-mile is 9 feet. The bog in the 

 Lachlan Swamp is about 9 or 10 feet deep in the centre, and 

 shallow at the sides. The depth gradually increases with the 

 course of the stream to about 30 feet near Botany, The sand 

 below the bog also increases in depth, but not in the same ratio. 

 Thus there is a rapid fall in the surface of the sandstone 

 formation towards Botany until we approach the northern shore 

 of Botany Bay, at which point the sandstone rock crops out 

 above the surface and is covered by a stratum of rich yellow. 



