DIAMOND FIELD OF THE GREAT LAKES 385 



This view also supposes that the glacial abrasion directly freed some of the 

 diamonds. 



Of course the two hypotheses might be conjoined and this would be reas- 

 onable enough if the diamond-bearing matrix were such as to be topographi- 

 cally protruding and be subjected to disintegration and wear during the inter- 

 glacial interval. 



Of the two hypotheses, I incline somewhat to the first, as I think it more 

 likely that the diamonds would be accumulated in some notable quantity in 

 the long preglacial period of disintegration than in the relatively short inter- 

 glacial interval. 



To me also it seems that the former hypothesis is the more 

 probable one, for the reason given, and further, because, as will 

 be seen from what follows, the broad fan of distribution of the 

 diamonds would seem to require a somewhat extensive area of 

 supply, unless it be assumed that this was very near to the 

 " center" from which the ice moved. 



THE ANCESTRAL HOME OF THE DIAMOND 



The problem of locating the area from which the diamonds 

 of the drift have been derived is a fascinating one, and, while 

 the data now available are insufficient for its complete solution, 

 they are of a kind to indicate that, with the increase of our 

 knowledge likely to come in the next decade, the desired end 

 may be reached. 



The first question which naturally arises is whether all the 

 diamonds that have been found in the lake region have been 

 derived from a common source. While there is no certain 

 evidence that they have, nevertheless it would seem to be prob- 

 able. Diamond-bearing rocks are not so numerous that there is 

 much likelihood of two unconnected areas being discovered in 

 the region in question. Moreover, the occurrence of diamonds 

 with somewhat similar crystal habits over so large a territory 

 would seem to be significant. The Oregon, Eagle, and Kohlsville 

 diamonds, since they were found in the Green Bay lobe of 

 the ice mantle, a comparatively narrow area, must certainly be 

 regarded as having a common source, and this must be, as the 

 writer pointed out in 1894, either on the medial line of the lobe, 



