32 



PSEUDOMORPHISM IN MINERALS. 



ing of natural glass, some of which is of just the same composi 

 tion as opal, and exhibits a somewhat similar play of colors. 



All the Tidal Creeks may be dammed, j-o as to keep out the 

 salt water and retain the fresh, and the water raised by appliances 

 for irrigation, as was proposed to the land owners of Doughboy 

 Creek fourteen years ago. 



The remedy for the past state of things, the droughts so fre- 

 quently experienced, lies in adopting the State-aid system, as in 

 vogue in Scotland, enabling land owners to obtain money for 

 special improvements on mortgage from the State. 



In the course of an examination of the minerals in the Queensland 

 museum special attention has been paid to those processes of 

 decomposition which have resulted in pseudomorphism, and as it 

 is a subject which, to judge from mineralogical reports, does not 

 seem to have been studied in Australia, it has been thought 

 desirable to invite the attention of the society to it by means of a 

 few illustrations drawn from Queensland mining-fields. The 

 present communication refers only to certain ores of copper 

 occurring at the Cloncurry mines. 



None of our waters, whether rain or spring, are the pure 

 chemical combination H 2 O — in its integrity it does not indeed 

 exist in nature ; natural water always contains in solution 

 extraneous gases or solids derived from the atmosphere or the 

 earth. The usual compounds introduced from these sources are 

 carbonated alkalies, double carbonate of lime, magnesia, or iron 

 oxides, silicates of alumina, common salt, and nearly always 

 minute percentages of ammonia. Probably from the oxidizing 

 action of electric discharges upon the last element small quantities 

 of saltpetre and soda nitrate are also communicated. 



One portion of the rainfall rises again immediately by 

 evaporation to perpetuate the circulation of moisture. The other 

 is more permanently absorbed and re-appears eventually as spring 

 water. The latter portion in its passage downwards through 

 clefts and fissures acts upon the materials in its path with forces 

 which are irresistible. The most compact mineral and rock 

 masses yield to the unceasing action maintained in its descent, 



PSEUDOMORPHISM IN MINERALS, 



By H. F Wallmann. 



