XY. GEOLOGY AND MINERALOGY. 133 



The effect of chemical action, sometimes combined with physical 

 action such as heat, is exemplified by the decomposition of 

 minerals and rocks, the deposition of minerals from solutions, the 

 change of minerals into other minerals, or pseudomorphism, the 

 change of rocks into other rocks, or metamorphism, &c. 



This collection, which is rapidly being increased, has re.;;ently 

 received specimens illustrating phenomena of considerable interest 

 as contributions to the puzzling questions of the formation of 

 minerals and mineral veins. These tend to show that in some 

 mineral veins in which quartz apparently stands alone as the 

 usual matrix of gold, carbonate of lime was formerly the matrix, 

 but has been removed in solution leaving quartz and gold only, or 

 in some instances has been replaced by quartz as a pseudomorph. 



To this collection are appended, as illustrating part of Chemical 

 Geology, some specimens of artificially formed minerals such as 

 boiler deposits, furnace products, stalactites and stalagmites 

 formed from building materials, spring deposits, &c. 



VIII.— COLLECTION ILLUSTRATING THE MODES OF 

 OCCURRENCE OF MINERALS. 



Although the Museum possesses a large general collec- 

 tion of minerals, which can be examined by students of 

 mineralogy, it has been found profitable, in the interest of mining 

 students, to exhibit the ores and valuable products of Australia, 

 in such a manner as to give a recognised individuality to 

 what is called a mineral deposit or an ore deposit. Thus, when 

 possible, the ores have been accompanied by specimens of the 

 local rocks, specimens of eruptive rocks occuring in or near 

 the deposit, and specimens of minerals found in close association 

 with the ores. This mode, no doubt, will command the attention 

 of the mining community from an educational point of view. 



IX.— COLLECTION OF GOLD SPECIMENS. 



The collection of Alluvial Gold includes a number of 



models of large nuggets for which the colony of Victoria is well 



known. The largest represented is the " Welcome" (2,195 ozs.), 



of an approximate value of £8,780, found at a depth of 180 feet 



J 



