Reviews — J. Arthur Fliillipi Ore-Depoaits. 35 



usually of comparatively recent date, and are generally not older 

 than the Tertiary period. Localities in which alluvial detritus is 

 washed for gold are known as placers, but when tinstone is the ore 

 sought after they are called Streamworks. 



"The ores of iron and manganese are almost the only metalliferous 

 minerals usually occurring in stratified beds, those of nearly all the 

 other metals being obtained from some other variety of mineral 

 deposits. 



"Although aluminium and magnesium are now regularly produced 

 upon a small scale, they can scarcely be classed among metals derived 

 from metalliferous ores in the sense in which that term is usually 

 understood. The same may be said of sodium, which is chiefly 

 employed in the preparation of the two above-mentioned metals. 



" Metalliferous deposits are found in such varying forms, and under 

 such differing circumstances, that it might at first appear difficult 

 to classify them in accordance with theii- characteristic peculiarities 

 and modes of occurrence. A careful study of their origin, structure, 

 and composition appears, however, to justify their division into the 

 following groups : — 



y „ (a. Deposits formed by tlie mecliamcal action of water. 



1. SUPERFICIAL. I ^_ Deposits resiilting from chemical action. 



[a. Deposits constituting the bulk of metalliferous beds 

 I formed by precipitation from aqueous solutions. 



j-p „ ] b. Bedso riginally deposited from solution, but subseqeuntly 



li. bTKATiFiED. -^^ altered by metamorphism. 



I e. Ores disseminated through sedimentary beds, in which 

 (^ tbey have been chemically deposited. 



(a. True veins. 



b. Segregated veins. 



c. Gash veins. 

 TTT TT id. Irapregnntions. 

 III. Unstratified. <; ^ stol^kwVks. 



/. Fablbands. 

 g. Contact deposits. 

 \^h. Chambers or pockets." 



The author next proceeds to describe the nature of those ore- 

 containing superficial deposits which have been formed by the 

 mechanical action of water. 



He gives a graphic description of the auriferous gravels of Cali- 

 fornia and the method of obtaining the gold therefrom by hydraulic 

 mining. 



The gravels of Victoria, which are approximately of the same 

 geological age as those of California, more frequently represent the 

 beds of ancient rivers whose valleys have since been covered up by 

 volcanic outflows. Here hydraulic mining cannot be successfully 

 employed, and mining beneath the lava-capping has to be resorted to 

 instead (p. 7), 



The Tin Stream Works of Cornwall are well described, and present 

 many features akin to those in which gold instead of tin forms the 

 metal to be sought for. 



We next pass on to stratified rocks containing ore-deposits, such as 

 linionite, haematite, argillaceous ironstone and carbonate of iron, the 

 various kinds of which, with their mode of occurrence, are noticed. 



