BY SYDNEY B. J. SKERTCHLY. XV 



where they pass below the Chillagoe Limestone. Is the chief 

 home of all the mineral wealth. 



Age. — Dewnian. 



(8.) Thtnjdlonii lieih. — A series of highly metamorphosed 

 rocks, chiefly mica and hornblende-schist and gneiss. Flanks 

 the Herberton Beds to the south. Contains rich silver and 

 copper lodes, as fissure veins, in this differing from the typical 

 Chillagoe ore-bodies, which are carbonas. Gold not \incommon. 

 Tin at the Tate on the junction of these beds with the granite. 



Age. — Silurian, or possibbf older. 



III. DescriptiuH of Fiochs. — {« j Alluriuin. — The Alluvial 

 Deposits of N. Queensland do not call for detailed description, 

 consisting as they do, of the usual alluvial and gravel beds. As, 

 however, this part of the country has been dry land since the 

 close of the Cretaceous epoch, an enormous amount of denuda- 

 tion has taken place, which has left its traces in high-level 

 deposits which reach in places to 100 feet above the present 

 stream courses. Some of these still lie exposed to atmospheric 

 Avaste, other portions have been sealed beneath great basalt flows, 

 and constitute Deep Leads, such as that which yields so much 

 tin at Herberton. Of the unsealed deposits the extensive alluvial 

 workings of the Tate Tin Mining Co., form a good example. 

 The alluvial beds yield gold, tin and bismuth carbonate 

 (bismuthite) as commercial products. 



fh) Basalt. — The enormous flows of basalt which extend at 

 intervals throughout the length and breadth of the Colony, from 

 Cape York to N.S. Wales, and from the Pacific Coast westward 

 into South Australia, often covering many thousands of square 

 miles in continuous sheets, constitute one of the most interest- 

 ing features of Queensland geology. 



The basalt generally lies almost perfectly level, and must 

 have been poured out in an almost limpid condition of fluidity. 

 No geologist can traverse these rusty plains, with their choking 

 dust, without the impression crystallising into certainty that the 

 basalt was never ejected from ordinary volcanic vents, but must 

 have welled up from beneath through innumerable fissures or 

 dykes, and deluged the land in a fiery flood from 100 t3 300 feet 

 in depth. 



