29 



pressions on the dessicating muddy flats. Tlie water moved bjr 

 tlie wind laves tlie shore and contaminates itself with its own 

 rejectamenta. 



One property of the water of the Murray is the remarkably 

 low quantity of saline matter in solution, and its softness. 

 Water collected in January in a fast falling river yielded at 

 the rate of seven grains of dissolved earthy matter per 

 gallon, whilst the quantity of calcic carbonate was 3 '9 grains 

 only per gallon. 



ElVEE ALLUVITJiT. 



It has been stated that the river occupies only a small part 

 of the gorge, the rest being an alluvial deposit. The alluvium 

 of the banks consists largely of fine sand mixed with fine clay 

 in sufiicient amount that when the whole is moistened to admit 

 of being shaped into a cohering mass ; when dry, however, the 

 whole is perfectly incoherent. In the more inward-lying parts 

 of the alluvial tract more clay has accumulated. The materials 

 of the cliffs have not contributed, except in a partial way, to 

 the formation of the alluvium ; conspicuous among the con- 

 stituents of the alluvium are spangles of white mica, which 

 clearly indicate transport from a distance, as that mineral is 

 not present in the cliffs of the Murray until an inlier of 

 mica slate, fourteen miles north of Mannum, is reached ; a 

 distance of more than 300 miles from the Boundary. 



Mr. Pollitzer insists that the alluvium " actually is a marine 

 deposit" (p. 10). Whether his hypothesis, "that the gorge 

 was made by a salt-water stream formed by the receding sea," 

 demanded a marine dejDosit, or whether it was an inference 

 based on the fact " that if you bore a hole in these deposits 

 you will meet with brackish water, in spite of having fresh 

 Murray water within a few inches," I cannot say ; but it is 

 most certainly true that Mr. Pollitzer has ignored the evidences 

 of its fresh- water origin in the form of numeroiis shells still 

 living in the river and its lagoons, whilst the existence of 

 brackish water in the deposit admits of other explanation. In 

 fig. 2, plate III., which represents a cross section ot the gorge, 

 I show that the debris of the cliff adjacent to the lagoon is 

 interstratified with a clayey alluvium. The bed of talus, which 

 is composed of sand and angular pieces of stone, admits freely 

 the passage of water, whilst the contiguous clays confine it 

 within that stratum. The water in the taluses is derived from 

 the surface flow down the cliff -face, and in its passage takes up 

 salt from the calciferous sand-rock. As some evidence of the 

 appreciable quantity of the sodic chloride in the calciferous 

 sand-rock, I have to state that the steep face of the cliff occu- 

 pied by that rock is where protected by an overhanging ledge 



