BRAZILIAN DIAMONDS AND THEIR ORIGIN 615 



them on his wheel. The discovery of some of these caldeiroes after 

 expensive labors, some thirty years ago, afforded sufficient return to 

 enrich the families of the two partners who worked them. An eye- 

 witness to the fact relates that in one of the holes under the diorite 

 arch, when the superficial layer of sterile sand was removed, a clear 

 mass of the precious stones was revealed, and the discoverers were 

 able on the spot to fill their pockets with diamonds. In the Ribeirao 

 do Inferno, a single caldeiroe of a few cubic metres' capacity fur- 

 nished nearly 8,000 carats of diamonds. Such fortunes, however, are 

 extremely rare, and can not be counted on in the regular mining. 



It is easy to comprehend how powerful must have been the action 

 of the erosion above described, the duration of which is measured by 

 many millions of years, but is quite outside of our chronology. The 

 greater part of the ravine through which the Jequitinhonha flows, as 

 well as the whole groundwork of the hydrographic system of the 

 region, is doubtless due to phenomena of upheaval, the directions 

 of which oscillate around a north-and-south axis. The tributaries of 

 that river have cut out channels for themselves w r hich are now deep, 

 close canons, with sharply cut, precipitous walls. 



The almost horizontal disposition of the sandstone strata, and of 

 the conglomerates, which form the banks of the rivers, and the terraces 

 which indicate the successive levels occupied by the river-bottoms, 

 leave no doubt of the correctness of this assertion. At first, conse- 

 quently, the bottoms of the streams were almost at the level of the 

 surface ; the rivers overflowed their banks after light rains, and their 

 diamond-bearing sands were spread over the table-lands and in the 

 mountain-gorges. As the beds of the rivers were worn down deeper 

 in the rock, overflows became more rare, and the sands were carried to 

 only small distances from the banks. Finally, after a certain period, 

 inundations became impossible, and the sand was deposited in the 

 caldeiroes, the caves, and subterranean channels which the river wore 

 out in the rocks over which it flowed. This epoch may be referred to 

 the period which preceded our own, and which is characterized in 

 Europe by the stone implements of human origin and use, specimens 

 of which have been found in the diamond-bearing land. 



Then, either by a rising of the coast, or, as is less probable, by a 

 subsidence of the central plateau of Minas Geraes, the fall of the 

 streams diminished, and, instead of continuing to excavate their beds, 

 they began to fill them with the diamondless, shifting deposits, the 

 formation of which is continued into our day. The sands of the 

 table-lands and the banks of the rivers are much less rich than those 

 of the streams ; and in any case the diamonds have to be separated, 

 by methodical washings, from the foreign substances with which they 

 are mixed. Very rarely a simple sifting with the fingers suffices to 

 extract the jewel. In 1824 a region was discovered in the lower part 

 of the table-land of Diamantina where tjie diamonds were scattered 



