16 Anniversary Address. 



for the supposed origin of diamond in a plutonic rock. I bave 

 quoted the original words to prevent mistakes as to the meaning. 



DIAMONDS IN" BEAZIL. 



Brazil seems naturally to claim our first attention. It has been 

 found that in a certain Brazilian rock called ItaGolumite, diamonds 

 have been found in situ, and, therefore, all diamonds are assumed 

 to have been derived in a similar way, wherever a rock imagined 

 to be Itacolumite exists. 



Tn 1846, Professor Shepherd, of .South Carolina ( A. S. J. II., 

 253 ) announced the extensive development of the rock in that 

 State, and he gives a figure and description of a diamond from 

 gold washings in that formation. 



In Brazil, however, they occur in great numbers, in the lower 

 Itacolumite beds. 



According to Humboldt this rock belongs to the very oldest 

 sedimentary deposits. 



So far as my own observation has gone this rock does not occur 

 in New South Wales, and even in Brazil, as I will show, diamonds 

 are not confined to it. My friend Mr. Ulrich, late of the 

 Yictorian Survey, says the same of the sister colony, and assures 

 me he had very good opportunities of satisfying himself by 

 examinincT the Brazilian specimens at the last International 

 Exhibition at Paris. Humboldt {Essai Ghognostique Paris, 1820, 

 p. 89), includes Itacolumite in the quartz rock series parallel 

 with his primitive clay slate. 



Von Cotta places it among the crystalline schists, and describes 

 it as a fine-grained micaceous talcose or chloritic schist, sometimes 

 flexible, holding occasional quartz pebbles with magnetic iron and 

 gold, as well as diamond. According to Eschwege, it passes into 

 Itahiriie, which belongs to the Eed Hsematitic group. Other 

 writers include it with " Mica Schist," " Quartz of the mica slate," 

 and " Elastic sandstone." Heusser and Claraz consider it a 

 " granular quartz," sometimes bearing quartz veins with pyroph- 

 illite lim*^. 



Eschwege says it attains in Brazil a thickness of many thousand 

 feet, ranging for hundreds of miles. 



