386 W. H. HOBBS 



or still farther away to the northward. It is also fair to suppose 

 that the Saukville, Burlington, and Dowagiac stones, though 

 they differ from one another in habit as much as any three stones 

 from the region, have also a common source, since they were 

 located comparatively near to one another in the moraines of 

 the Lake Michigan lobe. Of these latter, the Dowagiac diamond 

 is a hexoctahedron, like the stones from Plum Creek and the 

 closely related vicinal hexoctahedrons of Eagle and Kohlsville. 



Provided a common source is assumed for all the diamonds 

 of the region, this can only be located at the apex of the fan of 

 diamond distribution on the hither side of the neve from which 

 the ice moved. The wider this fan of distribution is found to 

 be, the nearer is its apex carried towards the ice summit. The 

 radial sides of the fan must be largely determined from the 

 directions of striae within the Canadian wilderness, of which an 

 adequate number have been recorded only from the immediate 

 vicinity of the Great Lakes. Beyond these borders the tracking 

 of the diamonds can be carried out only with a certain approx- 

 imation to correctness. 



One of the results of the magnificent investigations of Tyrrell 1 

 and Low, 2 the one working to the west and the other to the east 

 of Hudson Bay, has been the location of two main "centers" 

 of the ice mantle corresponding to the Keewatin and Labrador- 

 ean or Laurentide glaciers. The eastern of these "centers" or 

 neves, and the one which must have principally affected the 

 glaciation of the area of the Great Lakes, has been located by 

 Low to the east of James Bay, a little to the eastward of the 

 present watershed on the Labrador peninsula. This is brought 

 out on the accompanying map (Fig. 2) by the directions of the 

 striae of this vicinity. 



The tracks of the lake diamonds which have been delineated 

 upon the map, converge in the direction of this neve, and show 



'J. B. Tyrrell : Report on the Doobaunt, Kazan, and Ferguson Rivers, and the 

 northwest Coast of Hudson Bay, Geol. Surv. of Can., Vol. IX, 1896, Report F r 

 pp. 1-218. 



2 A. P. Low : loc. cit. 



