* 
Geology and Mineralogy. 225 
In its lithological characters it resembles closely the upper 
quartzite of the Serra oe Itacolumi and probably belongs to the 
same geological horizo 
Two theories may be proposed to riers for the presence of 
the diamond in this quartzite. One that the diamond alread 
existed when the rock was consolidated sy chi entered into its 
composition like any other pebble; the other that the diamond 
was formed in the rock. At first sight the first theory appears 
the most probable one, but there are some reasons for giving 
more credit to the second. 
A third mode of occurrence was beet by Messrs. Heusser and 
Claraz at Sao Joio da Chapada r Diamantina, where the 
jiamoud is Se with a white ae analogous to lithomarge 
which occurs with veins of quartz containing specular iron, that 
traverse the quartzites 
It will be seen, therefore, that the diamond and topaz are found 
in the same rocks and geological position and with the same min- 
eral associates 
The other colored minerals or gems of Minas, viz: the beryl, 
atin spo odu umene, eget echt and. red and green 
consist of gneiss and mica-schists ue in places become graph- 
itic. The gems occur pri ncipally in loose gravel but have been 
traced to their original deposits in quartz veins traversing the 
oo schists 
I to be noted that of these minerals the tourmaline is also 
Paes with the diamond and topaz-bearing rocks, but in this 
case it 1s always the black variety, not the red, green or white 
varieties of the crystalline schists. 
In concluding this brief abstract of the very interesting inves- 
tigations of Prof. Gorceix, by far the most complete and serious 
studies that have ever been made of the geology of Minas and the 
who has now a press a memoir giving the results of his nal 
Is to be hoped he will have the catielaiaiin of completing his is 
studies and of setting at rest the long disputed questions in 
— to that most HOD Le: subject, the mode of origin an 
oceurrence of the diamond.—ditorial in Rio News, Rio de 
Somsiec, May 24th. 
