GEOLO(JICAL EXPLORATIONS AND LITERATURE— 1800. Hi) 



chaiacter, which iKiiidiiig is clue ti) its having Howed, the same as is seen in (lie baiul- 

 iug of the siliceous furnace slags. * * * It is this fluidal structure or banding 

 that is so often mistaken in the rhyolites, felsites, trachj'tes, and Jaspilitcs for the 

 planes of sedimentation. (V. (iO.) 



The ore associated witli the jaspilite is said to be a concentrate from 

 its magma. In places the rocks haA^e been shattered and tlieir cracks tilled 

 with ore throug'h the action of percolating water. Aftei- cooling, the jaspi- 

 lites were acted npon bv the waves, yielding a detritns that was dej)Osited 

 upon the underlying ore deposits, forming true sedimentary deposits, many 

 of which have been since worked for ore. 



Three kinds of ores are distinguished, magnetite, hematite, and martite. 

 The ore associated with the jaspilite is usually of the latter kind. 



The argument in favor of the eru|)tive origin of the ores and jaspi- 

 lites is outlined, and it is stated that in 1885 Charles E. Wright, at that 

 time State geologist of Michigan, had ^jroved to his own satisfaction that the 

 ores are eruptive. The author dismisses Irving's argument for their sedi- 

 mentary origin by declaring that he "starts out with either denying or 

 ignoring the occtirrence of the very facts which the present writer has 

 figured, and which caused him to hold the eruptive A-iew. A theory of the 

 origin of the iron ores that starts out with denying the facts that it ought 

 to explain can hardly be accepted until it recognizes these facts and explains 

 them'' (\). 71). 



After the eruption of the jaspilites and their denudation, other rocks 

 were forced through the strata in a molten condition. Diabases and 

 diorites were the first rocks introduced, and they added so much volume to 

 the already existing rocks that these were thrown up into folds. Many of 

 these diabases and other basic rocks have become schistose, but they do 

 not pass into sedimentary schists, as has been sttpposed by some observers. 

 "The two look closely alike and are similar to each other in coin|»osition, 

 but do not pass into one another any more than water and oil do, although 

 a hasty observer might not see the line of separation between tlie two" (p. 72). 



The author mentions that at the Cleveland mine and elsewhere the 

 "schistose diabase and diorite come in contact with the sedimentary schists" 

 (p. 72). 



