ON THE BARRIER RANGES SILVER FIELD. 179 



■development of the more basic minerals lead us from any point in 

 this progressive change into the various hornblendic rocks. These 

 •changes are often so gradual, that it would be almost impossible 

 to fix upon any as true rock types or define their lines of demar- 

 cation. 



In connection with the study of these rocks, it would be inter- 

 esting to extend the field of examination to the eastward, where 

 at a distance of 30 or 40 miles, a line of ranges not yet visited 

 appears to run in a northerly direction, and should if continuous, 

 form a junction with the Barrier Ranges between here and Mount 

 Browne. It is quite possible that the higher portions of the plain 

 may in some cases, represent the out-crops of rocks but slightly 

 •covered by the products of their own decomposition. These if it 

 were possible to examine them, might afford valuable evidence as 

 to the chances of again picking up this silver bearing formation 

 to the eastward, where if the anticline could be found, the study 

 •of the succeeding rocks dipping east might lead to very valuable 

 results. 



The irregular and sometimes semicircular trend of these elevated 

 portions of the plain might if carefully studied, be found to have 

 an important bearing on the question of underground currents 

 and reservoirs of water ; for instance, the drainage from the hills 

 takes a southerly direction across the plain, following extended 

 lines of greatest depression. In addition to this, the alluvial 

 deepens as we go south, proving the bed-rocks to have a consider- 

 able fall in that direction. Now if we admit, as I am inclined to do, 

 that the depressed portions are due to the settling and compression 

 of the deeper alluvial, and the elevations to the shallow deposits 

 ■overlying raised portions of the bed-rock, it stands to reason that 

 any extensive area of depression surrounded on the east, south, 

 and west sides by elevated country, and consequently opening to 

 the north, must if connected with the underground drainage from 

 that direction, contain accumulations of water proportionate to 

 the southerly fall of the bed-rocks and the area of the partly 

 enclosed basin. I have not yet had an opportunity of studying 

 this question in connection with the underground drainage of the 

 country, but there is no doubt such a study in a comparatively 

 dry country like this would be very interesting, not only to science 

 but to the public generally. 



It may be remarked that the presence of detrital iron ore, 

 scattered profusely over the tops of many of these raised portions 

 of the plain, would appear to favour the conclusion, that in some 

 cases at least, rocks may have outcropped along such lines, and 

 that during their decomposition by atmospheric and organic 

 agencies, their contained iron has been concentrated as ferric 

 oxide in nodules and irregular veins and masses, often forming 



