610 THE AMERICAN NATURALIST. [Vou. XXXII. 
feel grateful to Professor Goebel for the admirable manner in which 
he has presented them, and all will look forward eagerly to the 
appearance of the subsequent volumes, which we hope may not be 
long delayed. DoucLas HOUGHTON CAMPBELL, 
STANFORD UNIVERSITY, 
ay, I 
MINERALOGY. 
Genesis of the Diamond. — Derby ! has sifted the evidence of the 
Brazilian deposits bearing on the puzzling and as yet unsolved prob- 
lem of the origin of the diamond. Three localities are discussed, 
of as many types. : 
At the Agua Suja mine, in western Minas Geraes, the diamond- 
bearing bed is a decomposed conglomerate, both matrix and pebbles 
. having been transformed into clay. The fragments can, however, 
still be recognized as belonging to the various schists, granites, and 
sandstones upon which the bed rests, and to basic eruptives, prob- 
ably members of the nepheline-bearing series of rocks of the region. 
Weight is placed upon these basic eruptives as suggesting an anal- 
ogy with the South African deposits; on the whole, however, the 
differences are more striking than the similarities. The diamond is 
evidently contained in the cement, not in any constituent of the 
breccia, and its source cannot even be conjectured with any degree 
of certainty. 
In the mines of Diamantina and those of Grao Mogōl, all in Minas 
Geraes, which are the oldest and best known of the Brazilian fields, 
the diamonds occur in a quartzose rock known as itacolumite. There 
are two types of this rock, a schistose form, and a massive variety 
which the writer believes is clearly clastic, and later than the schis- 
tose form, resting unconformably upon it. Probably both types of 
the rock are clastic, but both are largely metamorphosed, and it is 
impossible to say whether the diamond is a local product of that 
metamorphism or was introduced as a clastic element. 
The third locality described is the mine at São João Chapada, 
near Diamantina. The description is very full, the place having 
never been described before, as its interest demands. It consists of 
a huge open pit, in a mass of clay produced by the complete decom- 
position of the country rocks. The clays may be differentiated 
1 Brazilian Evidence on the Genesis of the Diamond. Journ. of Geol., vol. vi, 
p- 121. : 
