CI 



surface of the country wherever a pre-existing cause intervenes 

 sufficient to arrest the passage of the aerial-borne material 

 These combined with the decomposition and redistribution oi 

 decayed vegetable matter may be said to be the prime agents 

 producing our soils. .,.',,. .i_ i • „i 



Travertine.— Next in the series building up the geological 

 structure of the district— or rather I am of opinion, with my 

 friend Professor Tate, they should be included as contem- 

 poraneous with the above-named deposits— are those depositions 

 peculiar to our country familiarly known throughout the 

 Province by the term " Crust Limestone. Deposits ot this 

 so-called crust limestone occupy considerable tracts throughout 

 the district. In many places it is rapidly forming incrustations 

 a few inches below the surface, whilst in others I have seen it 

 actually intercalated with the soil. _ 



These recent calcareous accumulations must be regarded as 

 aggregations of limy material derived from the debris ot 

 older tertiaries, and limestone beds of the older fundamental 

 rocks together with magnesia derived from the decomposition 

 of clay-slate and other rocks of the old series, reduced to a 

 state of solution by the action of rain and sprmg-water perco- 

 lating through the "soil and subsoil, and other strata ; then by 

 evaporation the liquid passes off in vapour, and the precipitate 

 forms an irregular incrustation over, or near, the surtace. 

 Concentric structures of nodules frequently enclose fragments 

 of foreign matter, land shells, &c. By chemical analysis its 

 composition has been determined to be a carbonate of lime and 

 magnesia, therefore the more appropriate name by which it can 

 be designated is that of " Dolomitic Travertine. To the 

 curious in such matters I will here direct attention to a very 

 fine section— the formation of which was still going on until 

 arrested about 26 years ago by the erection of flour mills over 

 the site— on Smith's Creek, Section 4,160, Hundred of Munno 

 Para. 



Drift. 

 Character and Extent— Proceeding backward in time, the 

 uext formation which will occupy our attention differs essen- 

 tially from the preceding in so far that it has long ceased 

 actual formative activity ; I mean the mottled clays constituting 

 the subsoils of our plains, which are for the greater part of a 

 calcareo-argillaceous character. 



The deposit extends over nearly three-fourths ot the hun- 

 dred occupying uninterruptedly the whole of the western 

 portion of the district, as far easterly as Section 2,021 011 the 

 Little Para, and Section 1,723, Gawler South. As might be 

 supposed, it does not follow a direct alignment between the 

 points named ; nevertheless, omitting for the present three 



