GEOLOGICAL EXPLORATIOXS AND LITEKATIJKE— lS(iU. 43 



The author couchides his discussiou of the orig'iii of the ores liy the 

 statement that — 



the iron ores of the Hurouian series iu Michigan are essentially schists and heavy- 

 bedded strata, iu which none of the phenomena of aqueous deposits formed by precipi- 

 tation from water on the one hand, or by detrital accumulation on the other, are 

 wanting. They exhibit not only sti-atification, anticlinal and synclinal folds, but are 

 invariably traversed by systems of joints, and at many points exhibit a perfect slaty 

 cleavage. (P. 302.) 



As for the greenstone-schists and greenstone-shites, he declares that 



they — 



are intermediate in compositiou between clay-slate and hornblende-slate, and together 

 with the talcose aud chloritic slates, with which they are iuterstratifled, are probably 

 products of such a decomposition iu the wet way of the same crystalline sediments 

 which, entirely or less undecomposed, have gone to form those greenstones which 

 constitute members of the same series. (P. 303.) 



This means, we suppose, that the greenstone-schists were dej)osited as 

 crystalHzed sediments, and were afterward metamorphosed in the jjresence 

 of water. The paper concludes (p. 303): 



From a stratigraphical point of view, while evidence is elsewhere often obscure, 

 the Huronian greenstone, schists, and iron ores of Northern Michigan, in the absence 

 of close attention to their special chemical conditions, exhibit sedimentary and meta- 

 morphic phenomena adequate to render quite untenable, it is believed, the theory of 

 the exotic character of any portion of them. 



ISGG. 



Daddow, S. H., and Bannan, Ben.T. Coal, iron, aud oil; or the practical 

 American miner. Pottsville, Pa., 1866, pages 546-550. 



In connection with a discussiou of tlu^ iron ores of the United States, 

 Daddow and Bannan describe those of the Marquette region at some 

 leno-th. The productive magnetic masses of the district are believed to be 

 the result of precipitation. They are said to be uniformly stratified. 



The rocks which are intercalated with the ores are of volcanic origin, and though 

 not now reposing iu the form of dikes, they are true volcanic rocks, disintegrated by 

 coming in contact with water while iu a molten state. 



The authors quote a private report by Foster to the Iron Cliffs Mining 

 Company, in which, however, there is nothing recorded new to the 



