Explanation of Plates. 
273 
sources, and enabling a more exact delineation to be made of 
bowlder trains that extend outwards from these ledge areas 
upon and within the different glacial formations of the Rock 
river valley. 
It is but just to state in conclusion that the petrographic in¬ 
vestigations here outlined have taken the writer into a field 
new to his experience and that acknowledgements are due to 
Dr. W. H. Hobbs, of the University of Wisconsin, under 
whose instruction this work has been carried on, and whose sug¬ 
gestions have been of invaluable assistance in this presentation 
of results. 
EXPLANATION OP PLATES. 
PLATE VII. 
Map of the area including the Waterloo quartzite outcrops. 
Scale 1:99,566. Contour Interval 20 ft. The dark areos are 
quartzite exposures. 
i 
PLATE VIII. 
Fig. 1. Section, of Portland quartzite. In the upper left hand 
portion of the section is a cluster of quartz grains. Sericite and 
magnetite with finely granular quartz form the greater part of 
the interstitial material. x25. 
Fig. 2. Section of red quartzite. The quartz is in clusters 
of small grains with some more finely comminuted grains as 
interstitial matter, but the larger part of the interstitial mater¬ 
ial is sericite in elongated irregular forms. x25. 
Fig. 3. Section of Hubbellton quartzite. The larger quartz 
grains are in elongated forms with general parallelism in axial 
directions. They are often fractured and generally show un- 
dulatory extinction and peripheral granulation. The inter¬ 
stitial material is chiefly finely granular quartz. Sericite oc¬ 
curs in scattered areas with occasional grains of magnetite and 
zircon. x25. 
Fig. 4. Section of Lake Mills quartzite. The minerals and 
their arrangement are the same as in Fig. 3, but the quartz 
