DEP BASIC WEA S STV TiO CLES, 2 1G. 1 Y/ 
the quartzose bands along the northern border of the normal 
gabbro, are but phases of the latter rock, that a thorough field 
study of the relations existing between these rocks and the gab- 
bro does not seem necessary to their correct understanding, 
however much it may be desirable. All the field work which 
has been done in the neighborhood of Akeley Lake, however, so 
Fic. 4.— Preliminary geological map of the vicinity of Akeley Lake, Sec. 29, T. 65 
N., R. 4 W., Minnesota. From manuscript map furnished by Dr. U.S. Grant, of the 
Minnesota Survey. Scale, 3 inches to mile. 
far as it goes, confirms the conclusions of the microscope. A 
map of this region has kindly been furnished the writer by the 
Minnesota Survey through the courtesy of Dr. U.S. Grant. It 
is reproduced in Fig. 4. 
The rock south of the lake is the normal olivine gabbro. On 
its northern side this is in contact with the crystallized quartz- 
olivine-pyroxene rocks, to which reference has already been 
made (Vol. II., p.816). Onthe map they are marked “quartzite.” 
Between the main masses of the ‘‘quartzite” and the gabbro a 
