DIAMOND FIELD OF THE GREAT LAKES 38 1 



DISTRIBUTION OF THE LAKE DIAMONDS 



The localities at which the diamonds have been found are 

 distributed throughout an area nearly six hundred miles in 

 length by two hundred miles in breadth, with its longer axis 

 trending almost exactly northwest and southeast. Six of the 

 eight localities are near the center of this territory, within an 

 area about two hundred miles square, with its center near the 

 city of Milwaukee. 



All of the diamonds, with the exception of those from Plum 

 Creek, were obtained from the deposits of glacial drift. The 

 Plum Creek diamonds were obtained from the bed of the stream 

 in immediate proximity to glacial deposits. It is clear, there- 

 fore, that the stones must have reached their late resting places 

 in the drift through the agency of the ice mantle, and we should, 

 therefore, study the directions of glacial movement throughout 

 the region to discover the law of their distribution and to glean 

 any facts that may be within our reach regarding the ancestral 

 home, or homes, which they occupied before they were carried 

 away by the ice. 



The accompanying map of the lake region (Fig. I ) is based 

 on the glacial map of Chamberlin 1 , but revised and also extended 

 to the north so as to include the results of later studies. The 

 moraines in the vicinity of Lake Erie have been entered from 

 Leverett's Monograph, 2 and those southwest of Lake Superior 

 from a map by Todd. 3 The directions of the glacial striae have 

 been obtained from the works of Chamberlin, Leverett, and 

 Todd already mentioned, and from papers by Lawson, 4 Smith, 5 



'T, C. Chamberlin : The Rock Scorings of the Great Ice Invasions, Seventh 

 Annual Report U. S. Geol. Surv. 1885-6 (1888), pp. 145-24S, PI. VIII. 



3 Frank Leverett: On the Correlation of Moraines and Raised Beaches of 

 Lake Erie, Am. Jour. Sci. (3), Vol. XLIII, 1892, pp. 281-301. 



3J. E. Todd : A Revision of the Moraines of Minnesota. Ibid. (4) Vol. VI, 1898, 

 pp. 469-478. 



4 A. C. Lawson : On the Geology of the Rainy Lake Region. Geol. Surv. Can., 

 Vol. Ill, 1889, Pt. I, Rept. F, Sheet No. 3. 



S W. H. C. Smith: On the Geology of Hunter's Island, and Adjacent Country. 

 Ibid., Vol. V, 1893, Rept. G, Sheet No. 23. 



