37 



A Sketch of the Geology of the District 



AROUND MaNOORA, HUNDRED OF SADDLE- 

 WORTH. 



By Gatin Scoulae, Corr. Member. 

 [Eead April 5, 1881.] 

 Plate IV. 

 SupEEFiciAL Accumulations. 



A large reservoir at the Manoora Eailway Station presents 

 the following section : — Soil and subsoil, 10 ; clay, with some 

 gravel, 5 ; waterworn pebbles of schist, nodules of iron per- 

 oxides, &e., intermixed with clay, 5 ; total, 20 feet. 



Mr. F. Lindsay informs me that in a well he dug in these 

 superficial deposits, on section 266, at about fifty yards east 

 from the Eailway Eeservoir, a plenteous supply of water was 

 struck at a depth of 35 feet, permanently rising in the well to 

 the height of several feet. There can be little doubt but that 

 the superficial deposits, which occupy the valley of the Upper 

 Gilbert, are solely due to sub-aerial action ; and that the 

 retentive properties the gravels have for water may be reason- 

 ably ascribed to the decomposition of the immediately sub- 

 terposed fundamental clay-slates, which in their naturally 

 inexposed position have acquired the character of an imper- 

 vious clay, and tliereby check the downward flow of the water 

 permeating tlie superficial covering. It, thus, would appear 

 that the collecting and retaining properties of the water- 

 bearing area of the Upper Gilbert are solely confined to a 

 narrow strip of recent deposits flanking the bed of the present 

 water channel, and in no way is the supply of water derived 

 from the fundamental rocks 



Why sub-aerial superficial deposits should have become so 

 extensively developed, in many parts, over the fundamental 

 rocks in tlie valleys of the Upper Wakefield, Gilbert, and 

 Upper Light, is because the flow of water in these streams, is 

 now, and, for a long period past, has been only intermittent. 

 Consequently, vegetation during the non-flowing periods sprang 

 up and- occupied every favourable spot in the empty and water- 

 less channels ; and became a partial barrier to the onward 

 j)assage of the sedimentary material brought down by floods, 

 which otherwise would have been carried onward to the low- 



