224 : Scientific Intelligence. 
in a brown clay rock to which the gem-bearing veins appear to be 
confined. The other minerals accompanying the gems are quartz 
in fine crystals often pote! by the fee crystals, specular 
iron and very rarely euclases of which only seven or eight were 
found in the extraction eh several kilograms of topazes. a the 
other mines examined the conditions are essentially - same, the 
presence of ieskigts of me being noted in one o 
The topazes are generally of the well known vaio color 
with the lithomarge is so intimate that layers of this substance 
are often found penetrating the cleavage planes of the lag tals. 
Other crystals having the Spe pee. of topaz are brown and 
opaque or with a slight yellow varnish on the surface, aiehads 
well defined cleavage, and pass into a bluish schist which occurs 
in blocks in the mass of the unctuous schist 
The diamond acai to belong to the same geological horizon 
e 
vicinity of Ouro Preto but the diamond-bearing zone commences 
about sixty kilometers north of that city and extends almost due 
oe for a long distance, following the divide between the waters 
e Sio Franciseo and the coast rivers. The idea that the 
aes or the itacolumites form the primitive formation of the 
iamond is an old one and arose from the fact that these rocks 
are the predominant ones in the diamond region, but nel ither the 
gem nor its attendant tslnerala were seen by the early explorers 
in their oneal position. 
The origin of the diamond may be studied by means of the 
accompa ie minerals, which being more piesa: can more 
readily be traced to their place of origin. Of these, some may be 
regarded as accidentally associated with the and. but others, 
whose presence in the gem- — gravels is more constant, must 
be regarded as true sat Sage Among these last the minerals 
containing titanium such a anatase, rutile, rutile pseudomorph 
after anatase, and titanifenous iron hold the first place. To these 
are to be added black tourmaline, hematite i in the form of specular 
some 
The diamond pra oceurs in quartzite near the city of Grao 
Mogol, pat mining was at one time carried on. AS ecimen of 
pie! Wag containing a Shnend, has long existed in the national 
at Rio and two specimens Lah lately been obtained for 
the “nolles tion of the ane of Min The rock in these specimen® 
consists of irregular grains of aie wth flakes of mica or of the 
green substance, and ith Baie erystals among which is the 
diamon 
