334 Scientific Proceedings, Royal Dublin 'Society. 



to be certainly a diamond. My father then took it to Storr and 

 Mortimer, who confirmed West's opinion, and it was set in Wick- 

 low gold either by West or Storr and Mortimer. It is now an 

 heir-loom in my family. It is a nice diamond, not quite so large 

 as a swan-shot ; its only flaw being that it is slightly tinged with 

 yellow. There can be no doubt whatever about the authenticity of 

 the story." 



The rocks traversed by the Colebrooke river, in its upper 

 reaches, consist of beds referred to the Old Red Sandstone, and ap- 

 parently the Silurian formation is also represented close by. Now, 

 excepting South African localities, it would seem that the original 

 matrix of the diamond, in most of those countries where it is 

 found, is in rocks of these ages or somewhat older. It is true that 

 in Borneo both diamonds and gold are found in tertiary deposits ; 

 but there can be little doubt that neither the one nor the other 

 originated in them, but were derived from older palaeozoic rocks. 

 In India, too, the diamonds are generally found in diluvial de- 

 tritus, which is, however, largely made up of materials obviously 

 derived from rocks of possibly Devonian or Silurian age. 



In Brazil, according to a lately published account 1 , the mines 

 at Grrao Mogol and other localities are in a bed of palaeozoic age, 

 and at Parana they occur in Devonian sandstones and conglo- 

 merates. Mr. 0. A. Derby, the writer of this account, considers 

 that the diamonds, like the pebbles with which they are associated, 

 are all of detrital origin. But at Sao Joao the diamond is believed 

 to occur in its original matrix, namely, a vein of quartz called 

 barro, now decomposed, but containing iron and tourmaline. This 

 vein traverses unctuous schists and itacolumites, which are believed 

 to be of Cambrian age. 



Thus, in so far as the age of the rocks goes, there is sufficient 

 resemblance to the conditions of diamond occurrence in other parts 

 of the world, for saying that there is no inherent improbability in 

 the supposition that the diamond which is the subject of this 

 notice may have originated near the spot where it is stated to 

 have been found. ' 



1 American Journal of Science, February, 1882. 



