DIAMOND: OCCURRENCE IN BRAZIL 163 



of the more deeply situated diamond-bearing layer, to reach which it is necessary to divert 

 the water which flows over the barren layer. 



Although the diamantiferous " cascalho " is spread fairly uninterruptedly over long 

 stretches of the beds of streams and rivers, yet its distribution over the whole course of the 

 river is by no means regular. Here it may be accumulated in masses of great thickness, 

 there to only a sparing amount, while in a third place it may be altogether absent. 

 Moreover, the number of diamonds present in the material varies ia different rivers, 

 and in different parts of the same river ; it is recorded of certain rivers in the Diamantina 

 district, however, that the diamonds were so regularly distributed through the " cascalho "' 

 that it was possible to estimate with accuracy the weight in carats of the precious-, 

 stone which a certain amomit of this material would yield; this case is, however, very 

 exceptional. 



A large accumulation of specially rich " cascalho " at one particular point is the result 

 of the presence of certain conditions which exist only at that point ; such an accumulation 

 is sought for with eagerness. In the beds of the rivers cylindrical holes of greater or less 

 depth are sometimes bored in the solid rock by the action of the running water, such pot- 

 holes or "giants' kettles" being formed in the same way in many other parts of the world. In 

 addition to these, long channels, hollowed out of the bed of the water-course, and following 

 its course for a certain distance, or running obliquely across it, are also to be met with, 

 and are sometimes known as " subterranean canons.'" Such hollows in the bed of a stream 

 occiu* where the water has passed over softer beds, these being worn away to a greater depth 

 than are the surrounding harder rocks. The hollows so formed may be small or of 

 considerable size, and are often filled up with a specially rich " cascalho." In a small 

 hollow in the bed of the Ribeirao do Inferno, which joins the Jequetinhonha near 

 Diamantina, 8000 to 10,000 carats of diamonds were found, the neighbom-ing part of the 

 river-bed being very poor. Again, in a small pot-hole in the bed of the Rio Pardo, diamonds 

 to the weight of 180 carats were obtained by four negroes in the short space of four days. 

 Again, the three mines in the valley of the Jequetinhonha, which recently have been 

 specially prolific, namely, S. Antonio, with Canteiras above, and Acaba Mundo below, the 

 mouth of the Ribeirao do Inferno, were worked in depressions of the nature of channels or 

 " subterranean canons " in the river-bed. 



The valley-deposits (" gupiarras " of the Brazilians) are, as a rule, of small extent ; 

 they are formed of the same material as are the river-deposits, and the diamonds are 

 associated with the same minerals. This deposit is also known as " cascalho," and sometimes 

 also as " gurgulho " ; the latter term, however, is more often applied to the material of the 

 plateau-deposits. The valley-deposits also follow the direction of the present water-courses, 

 being situated at the sides of the valley above the present high- water level ; they are, as a 

 matter of fact, river-deposits laid down at a time when the bed of the river had not been 

 excavated to the extent it now is. In many cases the successive levels of the former beds of 

 the river are marked out on the sides of the valley by a series of such deposits or river- 

 terraces. 



The material of these terraces is much less worn than is that in the bottom of the 

 valley. As a general rule, it is found that the rounding of the rock-fragments is the more 

 pronoimced the lower is the level of the terrace in which they occur, and further that the 

 material of any given terrace becomes more worn the further it is deposited from the source 

 of the river. At the bottom of the same valley in which river-terraces are to be seen is the 

 present bed of the river with its deposits, the material of which is more worn and rounded 

 than that of any of the valley-deposits. It is therefore possible by means of this difference 



