Park. — Magmatic Segregation. 11 



stituting justice and their own Court to secure a convenient 

 verdict. The blot of Rangitikei-Manawatu will always lie on 

 the record of the Native Land Court, only surpasssed by that 

 of the Horowhenua, the judgment in which reads like one of 

 Horace's finest satires. Nor was the Native Land Court con- 

 sistent; and the deadliest comment on the judgment in the two 

 blocks referred to is furnished by the same Court's judgment in 

 the Manawatu-Kukutauaki cases. 



Art. II. — Magmatic Segregation in its Relation to the 

 Genesis of certain Ore-bodies. 



By Professor James Park, M.A.Inst.M.B., M. A.Inst. M. and 

 M. (Lond.), F.G.S., Director Otago University School 

 of Mines. 



[Read before the Otago Institute, 13th September, 1904.] 



Ore-deposits are of diverse form and composition. They 

 are found as true veins, as detached masses, and as members 

 of a sedimentary formation. It is now known that their mode 

 of occurrence, and, to some extent, their composition and 

 form, are determined by the prevailing geological conditions. 



In the past decade a vast mass of facts has been added to 

 the literature of the subject, particularly in America, where 

 the magnitude of the operations connected with mining has 

 afforded great facilities for observation and research. 



The genesis of ore-deposits presents many difficult pro- 

 blems, and naturally the literature of the subject is rich in 

 theoretical deductions. The introduction of petrographical 

 methods of investigation, and the demonstration of the prin- 

 ciple of metasomatic replacement, marked a new point of 

 departure, and led to a truer conception of the formation of 

 ore-deposits than had formerly existed. 



In this investigation we must remember that existing con- 

 ditions are but a reflection of the past. The agencies that 

 built up the crust of the earth in its present form are still in 

 operation, and still governed by the same natural laws. We 

 are living on the edge of a geologic epoch, and if we would 

 rightly understand the past we must study the present. The 

 occurrence of ore-deposits is merely a geologic happening — an 

 incident in the tectonic arrangement of the materials forming 

 the outer shell of the globe. Recent petrographical investi- 

 gation has shown that ore-deposits are always more or less 

 intimately connected with igneous rocks. This constant 

 association naturally leads to the broad generalisation that 



