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MUSEUM OF COMPARATIVE ZOOLOGY. 



29 



district visited by us. Associated with these rocks is the jasper, which 

 is acknowledged on every hand to be an inseparable part of the iron ore 

 formation. The origin of one gives the origin of the other. Their 

 interdependence is such, and has been so regarded, that- the relations 

 of one to the country rock give the relations of the other. The two 

 have been so fully described in the past, that it is only necessary to 

 briefly describe them here. 



The connnon form is that of interlaminations of jasper and iron ore, 

 the laminte varying from extreme tenuity to considerable thickness. In 

 some places the jasper predominates, in others the ore. In the hist case 

 we have a more or less valuable ore, according to the amount of the sili- 

 ceous material, which, however, may exist only in a mere trace. The 

 l)urer parts form large masses, that are mined, and which graduate into 

 the jasper, or ore containing so mucls jasper as to be unfit for working. 

 The workable parts are frequently lenticular in form, although often 

 irregular. The irregularity of the ore mass, its passage into the jaspery 

 ores, and the uncertainty where the next mass will be found, are amon(>* 

 the chief difficulties of the miner. The origin of the jasper and ore 

 becomes then a problem of great economic importance, as do also the 

 relations of both to the country rocks. Tlic permanence and extent of 

 the formation, whether it is in the form of vein deposits, eruptive (intru- 

 sive or overflow) masses, or sedimentary deposits, are questions in which 

 the capitalist and minor, whether they Avill or not, are most deeply 

 interested. As tliey have never been regarded as vein deposits, there 

 remains for us only the question whether the jasper and its associated 

 ores are eruptive or sedimentary in origin. 



Lest there be some misunderstanding as to to the reason for thus dis- 

 missing the theory of the ores here being vein deposits, we would remark 

 that the question has been ably and fully discussed before in the works 

 of previous observers. Furthermore, while veins on a small scale are 

 occasionally seen, we were unable to find upon cither the jasper or its 

 associated ore a single cliaracter belonging citlicr to a vein or an infil- 

 tration deposit. It therefore seems unnecessary to discuss the vein or 

 infiltration theory here. 



As both the eruptive and sedimentary origin of the jasper and the 

 ore have been advocated by some of the most eminent Kcolo^jists in this 



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country, it is necessary that the question should be answered by the 

 facts, and not by any preconceived theory or idea. The question now is 

 what are the flicts, and their most probable explanation. The first and 

 most important thing to be observed in deciding this is the relation of 

 the jaspery formation to its country rocks. 



