-■^h:^-^. 

 \-:--ji 



20 



BULLETIN OF THE 



others undergo great changes. Marble passes into quartzite, which in 

 turn graduates into novacuhte ; diorites, almost porphyritic, are the 

 equivalents of soft magnesian schists." (/. c, pp. 83, Si.) 



The '* soft hematites " are thought to result, perhaps, from the decom- 

 position of a 'Himonitic siliceous schist," with which they are associated. 

 *'It is not at all improbable that this change may have been brought 

 al)out by the alkaline waters of former thermal springs." (/. c, pp. 



90, 91.) 



The ''diorites" arc said to graduate from a heavy, tongh, black 

 variety into a soft, light-colored rock, resembling chloritic schist more 

 tlian anything else, and called by him dioritic schist. *' The bed- 

 ding of these rocks is generally obscure, and in the granular varieties 

 entirely wanting. It is usually only after a full study of the rock in 

 mass, and after its relations with the under and overlaying beds are 

 fully made out, that one becomes convinced, whatever its origin, it 

 presents in mass precisely the same phenomenon, as regards stratifica- 

 tion, as do the accompanying schists and quartzites No reference 



is here made to tlie false stratification or joints, which are numerous and 

 interesting, but which unfortunately, for want of space, can receive no 

 other attention here than to warn the observer against mistaking j/V/^V^ 

 planes for heddlng planes, which is sometimes done, even by experienced 

 observers." (/. c, pp. 102, 103.) lie also states that in no case has he 

 abserved a Huronian diorite in the Marquette district that does not con- 

 form " with the schistose and slaty strata with which they are associ- 

 ated." (/. c, p. 15G.) 



The rocks associated with the hard ores and ''diorites" are called 



''magnesian schists (mostly chloritic)." lie says regarding them : *' It 

 would be difficult for a skilled lithologist, and impossible for me, to draw 

 the line between the chloritic schists here considered and the dioritic 

 schists." Regarding the chloritic schist at one locality associated with 

 ''specular slate ore," it is stated : " Prof. Tumpelly has suggested that one 

 may be a pscudomorph after the otlier. In this comiection it may bo 

 remarked that no gradual transition of one into the other was observed, 

 the division planes being in each instance sharply defined." Q. c, pp. 

 104, 105.) 



Eegarding the connections of the ore in the Larnum nunc with that 

 in the Lake Superior mine, he writes : "It shows that such formations 

 are not vein or dyke-line deposits, but true stratified beds, like the 

 rocks by which they arc enclosed. Their structure is therefore essen- 

 tially the same as the coal, limestone, sandstone, and slate-beds, which 



