Secondary Beds of Northern Australia. 125 



ravel the history of the continent during this epoch, and 

 much valuable information may perhaps be obtained by 

 pointing out the questions requiring solution. 



1. Does the depression in which these secondary beds 

 have been deposited extend across the continent as an arm 

 of the sea, or is it a large inlet, and if it is the latter, where 

 does it terminate ? 



About 100 miles south of the route followed we have the 

 watershed between the streams running to the north, and 

 those running south into Cooper's Creek. This is a likely point 

 for the supposed inlet to terminate, and it should be examined 

 to see if the silurian rocks stretch across from the coast range 

 to the M'Kinlay Ranges. If the depression has been an arm 

 of the sea running from the north to the south coast, and 

 dividing the continent into two or more islands, by what 

 line does it reach the southern coast ? This ought to be 

 readily traced, for the horizontal sandstones may be 

 easily distinguished from the silurian sandstones with 

 vertical cleavage even by an inexperienced eye. Can these 

 beds underlay the alluvium of the Lachlan and Lower 

 Murray plains, or do they find a passage to the westward by 

 the valley of Cooper's Creek, dividing the M'Kinlay Ranges 

 from the Barrier Ranges west of the Darling ? 



2. Does the M'Kinlay Ranges form the western boundary 

 of the inlet or strait, or has this range formed a promontory 

 projecting into or been an island in the secondary sea \ 



This question as to the extension of the secondaiy rocks 

 to the westward is a very interesting one. All I have 

 been able to make out is, that the silurians are found on the 

 Gregory, and the upper waters of that river are running 

 through basaltic plains. The secondary rocks must be 

 found to the westward of this river if they extend in this 

 direction. 



3. Has the secondary formation originally extended over 

 a much larger area than it now occupies, and* since been 

 denuded ? 



If such has been the case, some patches of these secondary 

 rocks will most likely be discovered mixed with the ad- 

 joining silurians, or at least some fossils may be found, 

 indicating these rocks have covered the silurians. 



Judging, however, from the undisturbed character of these 

 rocks, and the absence of rolled drift, or any indication of 

 strong denuding action, I believe this question will eventually 

 be answered in the negative. 



