114 THE MAKQUETTE lEON-liEAKIXG DISTRICT. 



('ruj)tivc.s, tlie latter liivviny lieeu pouretl out on tlie bottom of the ocean. 

 The siHceoiis sediments are thought in part to have been produced through 

 the decomjiosition of the eruptive masses, in part to have come from the 

 surrounding land as erosion detritus, and in i)art to have been formed by 

 the accumulation of the remains of organisms. The iron ore associated 

 with these rocks is thought to have been deposited from springs whose iron 

 constituent was derived by solution from the eruptive rocks. The chemical 

 processes concerned in the formation of the ore beds were supposed to l^e 

 the following: The basic eruptives contained iron as oxide and chloride. 

 Its chloride was dissolved in the sea watei', and from this dilute solution 

 the iron was precipitated as an ocherous deposit of the hydi'oxide. This 

 was subsequently dehj^drated and changed into hematite. Stelzner, in the 

 review of the article, declares that the theory rests upon tlie assumption 

 that the diorites associated with the ores are eruptive, and this he states 

 had not yet been proved. 



Williams, G. H. Some examples of the dynamic metamorphism of the ancieut 

 eruptive rocks on the south .shore of Lake Superior. Proc. Am. Ass. Adv. Sci., 

 thirty-si.vth meeting, 1S8S, pages 22.J-226. 



In this preliminary notice of the results of microscopical work on 

 the ]\Iarquette banded green schists Williams states that this series of rocks 

 owes its schistosity to pressure and not to original bedding. The rocks are 

 believed to be squeezed and stretched eruptives. The reasons for these 

 conclusions and the descriptions of the observations on which they are 

 based were not published in full until 1891. 



BiKKiNBiNE, John. Iron ore mining in 1SS7. Mineral Resources of the United 

 States, calendar year 1S87, Washington, 1888, page 34. 



This author, in connection with statistical tables showing the ore 

 production of the various American iron-ore districts, incidentally refers to 

 the deposits of the Lake Superior mine as lying in "a synclinal fold 

 trending east and west, the western extremity outcropping." The entire 

 deposit is said to be underlain by chlorite-schist and to be overlain by 

 hematite-jasper. 



