124 Secondary Beds of Northern Australia. 



at first mistaken. All these forms could be seen on the 

 same ridge, but the trenches proved that this change only 

 affected the surface, and did not penetrate to any depth. 



The prevailing rock was a sandy schist, but bands of 

 slate with vertical cleavage, and masses of porphyritic and 

 granitic rocks, were mixed with it. Patches of dolomite, both 

 in the grey compact and white crystalline form, were also 

 met with at intervals. No fossils were found in these 

 rocks, so that their exact position cannot be determined; but 

 I have no doubt ^as to their being Silurians, which have 

 undergone metamorphic action, similar to that affecting the 

 same formation in the coast range. 



Traces of copper pre are found in great abundance, and 

 one very rich and extensive deposit of red oxide of copper 

 has been partially opened ; while, considering the small area 

 yet explored, it is probable many productive mines will be 

 discovered in these ranges. Even now there will soon be a 

 large mining establishment on the river, down whose banks 

 Messrs. Burke and Wills toiled in their journey to the Gulf. 



One singular fact noted in these ranges was the distance 

 to which the heat had penetrated into the ground. In a 

 shaft sunk to a depth of fourty-four feet there was no 

 diminution in this heat. When leaving the hot midday sun 

 of the tropics, going down this shaft produced a feeling 

 similar to that sustained on entering a Turkish bath. The 

 rock at the bottom felt warm to the hand, and in two or 

 three minutes after reaching it the perspiration burst from 

 every pore. 



It will be interesting to mark the depth at which a mean 

 temperature will be found in this mine. 



However incomplete these observations — made during a 

 hurried journey, and for the most part from the saddle — 

 necessarily must be, they yet establish the fact that between 

 the coast range and the M'Kinlay Ranges there has existed 

 a deep depression or valley, extending from the Gulf of 

 Carpentaria to the twenty -first degree of south latitude, and 

 that this depression was filled by the sea during the 

 secondary era for a period long enough to allow of the 

 deposition of the sandstone beds, from whence the fossils 

 described by Professor M'Coy have been obtained ; and 

 further, that these secondary beds show no indication of 

 disturbance, or of active denudation. 



Limited as this knowledge is, it may form a starting-point 

 for other observers, whose accumulated discoveries will un- 



