84 Armitage, Country about West Essendon. [^''^Se f ^*' 



Where the thalweg of this valley crosses Buckley-street, the 

 dark-coloured clayey nature of the surface soil, combined with 

 its manner of developing sun-cracks on drying, indicates that an 

 Older Basalt exists immediately beneath the surface, and that 

 the soil is, in part at least, derived from it. This indication is 

 substantiated by the evidence procured while the sewering of 

 this area was in progress. 



Between section viii., parish of Doutta Galla, and section 

 XX., allotment 2, parish of Cut-Paw-Paw, the Saltwater River 

 makes a broad, sweeping curve, known locally as the " Horse- 

 shoe Bend," a typical river meander. The surface of the 

 Newer Volcanic basalt on the river cliff' on the north side of 

 this meander is about 140 feet high,* while at a distance of 

 a mile to the southward, on the opposite side of the valley, the 

 top of the basalt plain is about 10 feet lower. This slight 

 difference in elevation, combined with the fact that the character 

 of the basalt is practically similar on both sides of the valley, 

 points to the conclusion that when the lava sheet had been 

 formed it was continuous right across what is at present the 

 valley of the Saltwater River. The pre-existing drainage system 

 of the country was completely obliterated by the lava floods. 

 The surface of this lava sheet would have, in general, a fairly 

 level character, with a gentle slope to the southward, and would 

 be swampy. These swamps would drain by overflow to the 

 south. Gradually drainage channels of a tortuous character 

 would originate on the young lava plain. One of these would 

 become dominant, having a meanderine course where it slowly 

 traversed the swampy areas. This main stream would gradu- 

 ally sink its channel by corrasive activity into the lava plain, 

 retaining, on the whole, its original meanders. During the 

 trenching of its valley, pauses in the vertically corrasive activity 

 of the stream would occur. These cessations of activity would 

 probably be due either to a movement of subsidence of this i)art 

 of the earth's crust or to the fact that a rock-bar lower down 

 was resisting removal by the stream's activity. During these 

 pauses in vertical corrasion the main energies of the stream 

 would be expended in the work of widening its valley by lateral 

 erosion. This work would proceed sufficiently far for the river 

 to aggrade its vahey floor by the formation of alluvial flats on 

 the insides of bends. Then, from some cause, such as an uplift 

 of the land, or the completion, down-stream, of the removal of 

 a rock-bar on which the river had been engaged at work, vertical 

 corrasion would recommence, and continue until an entrenched 

 meander had been sunk in the last-made flood-plain and also 



* The heights mentioned are obtained, where possible, from Contour Plan (2). 

 Other heights have been estimated from readings taken by aneroid, kindly lent 

 by Professor Payne, Melbourne University. 



