614 THE POPULAR SCIENCE MONTHLY. 



cupy for most of them have been worked the beds of all the water- 

 courses, but they were also placed in beds on the table-lands and in the 

 gorges of the mountains, at levels which the waters never reach in our 

 day, even in times of freshet. They have a peculiar appearance, that 

 never deceives the eye of the experienced miner. At first sight, they 

 resemble the gravels of our rivers. They are formed of rounded peb- 

 bles of various colors, and are composed of numerous species of min- 

 erals, of which I, still only at the beginning of my studies of the sub- 

 ject, have already recognized more than thirty. Of these, quartz, the 

 oxides of titanium, titanic iron, tourmalines, phosphates, fibrolite, octa- 

 hedric oligist iron, and magnetite, which are well known to the miners 

 and distinguished by them under various fanciful names, are the true 

 satellites of the diamond, its veritable train, and are with rare excep- 

 tions sure to be found with it at Diamantina. They have so intimate 

 a connection with it, in fact, that we are justified in believing that the 

 same formations include the primitive beds both of these minerals and 

 of the diamond. The form of the specimens leaves no doubt as to the 

 causes to which they owe it. They have been brought down by the 

 waters and worn round by friction. They can not, however, have been 

 turned into spherical balls by a simple transport of a few hundred 

 yards. The diamond itself, the hardest of all bodies, has not escaped 

 this action ; and fragments of it are found from which every trace of 

 crystallization has disappeared, and which are as round as marbles. 

 Not the sands of the large streams alone, but also those of the smallest 

 brooks, even those near their sources, present the same characteristics. 

 The stones must, then, owe their shapes to the polishings which they 

 have suffered by being held in the windings of the rocks and rolled 

 around them by the eddies of the waters. While they have been thus 

 polished off, they have produced an analogous phenomenon on the bot- 

 toms of the rivers, where they have caused the wearing out of those 

 circular holes the " giants' pots," the caldeiroes of the diamond-hunt- 

 ers, with which the beds of the streams of Diamantina are pock-marked. 

 The sands in these holes are naturally richer than the other sands ; for 

 the lighter elements are carried away by the water, and more fragile 

 substances than the diamond are ground to powder in them. For a 

 hundred and fifty years the miners have considered it a piece of great 

 good fortune to discover one of these caldeiroes ; but new ones are now 

 very seldom found. A few hundred yards above the bridge of the 

 Diamantina road over the Jequitinhonha, the course of the water is 

 barred bv enormous blocks of diorite, between which the current has 

 excavated subterranean passages. The river having been partly turned 

 from its course, one may now go into one of these grottoes, which is 

 occupied by a cascalho of extraordinary richness. The sides of the rock 

 are as polished as the best-worked marble ; the light of the torches is 

 reflected as from a glass ; and the visitor perceives at every instant cy- 

 lindrical holes as regularly formed as if some skillful potter had shaped 



