172 THE MARQUETTE IKON BEAPJNG^ DISTRICT. 



j^roduets. Occasionullv chlorite is present. Tliis ajipears from its shape to 

 have been derived from hornblende, but no nn(h>uV)ted ainphiboles have 

 been detected in the northern gi-anites. With few exceptions the rocks 

 are all biotite-granites or g-ranitites. The accessories are small crystals of 

 sphene, some leucoxene and magnetite, and an occasional zircon. 



The original constituents of the granites require no special description. 

 The ortlioclase and plagioclase are altered to kaolin, sericite, and calcite. 

 These products, together with a red earthy ilust, pr(il)ably an ocher, are so 

 thicklv clustered that they very nearl}' obscure the twinning bars of the 

 plagioclase and cause it to be confounded with the ortlioclase. The biotite 

 was originallv a Ijrownish-green variety. At present but few remnants of 

 the mineral remain. It has been changed to single plates and aggregates 

 of flakes of a pale to bright green chlorite, polarizing with blue tints. This 

 chlorite is sometimes intergrown with nuiscovite, but only in those cases 

 where the latter is evidently a product of dynamic action. 



The quartz appears in two forms, either as irregular grains of the usual 

 character of granitic quartz or as little masses filling triangular areas 

 between the other components and sending arm-like projections into them. 

 Some of it is in all probability original; much of it is unquestionably sec- 

 ondary. All of it is marked by the undulatory extinction, and a part of it 

 is completely shattered. 



No specimen of the granites examined is free from the effects of mash- 

 ing. In every slide placed mider the microscope more or less distinct traces 

 of dynamo - metamorphism are recognized. The feldspar is granulated 

 peripherally and the quartz is more or less completely shattered. The 

 fragments thus derived are mingled with chlorite flakes, epidote grains, and 

 occasionally a little muscovite, and the whole is cemented by newly formed 

 feldspars, among the most prominent of which is microcline. This mineral 

 was evidently formed in large quantity after the crushing of the original 

 minerals of the granite. It inserted itself into every crevice and space 

 between these; in some cases it has even formed tiny veins cutting across 

 quartz grains. 



Not only is microcline present in this fragmental aggregate, but it 

 occurs also as colorless rims around the cloudy ortlioclase, and also often 



