18 THE JOURNAL OF GEOLOGY. 
repetition of bands of these two rocks intervenes, so that the 
gabbro area appears to pass gradually into the ‘‘ quartzite” area. 
Two large bands are shown on the map, to the east of the lake, 
but these bands are not composed exclusively of the quartzose 
rock or of gabbro. The gabbro band contains on its borders small 
bands of ‘‘quartzite,” while the large “quartzite” band is inter- 
laminated with several narrow bands of gabbro. When thick 
these interbanded gabbros are similar in every respect to the 
normal gabbro further south, except that they may contain more 
hypersthene; when thin they are basic or granulitic phases of 
this rock. 
The quartzose rocks contain a large quantity of gabbro 
material, such as olivine, diallage, hypersthene, etc., which can 
only have come from the gabbro in contact with them. The 
origin of these rocks has not yet been worked out. 
Of the specimens indicated on the map No. 944, from the 
southern edge of the northern ‘ quartzite” area is a quartzose rock 
saturated with gabbro material, and interbanded with narrow 
seams of granulitic gabbro. No. 495, near the contact between 
this rock and the large gabbro band, is a-granulitic gabbro, with 
a diabasic structure in places. No. 946, from the center of this 
band, and No. 948, from the easternmost island in the lake, are 
normal gabbros containing some hypersthene. No. 947 is like 
No. 944. 
Before concluding this discussion it seems necessary to refer to 
some misconceptions that have arisen with respect to the author’s 
position regarding the Pewabic quartzite.‘ In the nineteenth 
report of the Minnesota Survey he describes a few specimens 
sent him by Professor Winchell from the vicinity of Akeley Lake. 
y 
Some of these were labeled ‘‘ Muscovados”’ and others ‘‘ Pewabic 
J 
quartzite,’ and were referred to under these names in the annual 
reports of the Survey. The ‘‘muscovados” were found, upon 
microscopical examination, to be mainly phases of gabbro, and the 
” 
‘‘quartzites’’ to include two distinct rocks, viz., granulitic and 
*W.S. BAYLEY: Nineteenth Ann. Rep. Geol. and Nat. Hist. Survey of Minn. 
Pp. 193-210. 
