0. A. Derby— Oa 



of the Diamond in Brazil. 37 



regular from top to bottom, while others present constric- 

 tions as represented in the diagram. The upper levels of these 

 pot-holes had been worked out by former owners and were found 

 rilled with new unproductive gravel but in the lower levels rich 

 virgin gravel was found. 



At Santo Antonio the caiion occupies the whole width of 

 the river-bed and has even widened out below so that the 

 walls are overhanging. The river has here cut through the 

 upper quartzite so as to meet the junction of the two series at 

 about the present natural level of the river-bed. Flowing 

 along the strike of the lower series, it has encountered the thin 

 layer of softer beds of schists and schistose qnartzites which 

 form the floor of the cavern, enclosed between the more mas- 

 sive beds which form the walls. The canon which is about 

 Inn feet deep was rilled with fallen masses of rock and gravel 

 which had been removed at the two extremities of the work- 

 ing, but a large rock- tightly wedged in between the walls, and 

 which had formed a small fall in the river, had been left, and 

 shored up by stout wooden braces, while work was being 







c Acnha-Mundo canon is similar in many respects 

 nto Antonio, but is remarkable in being transverse to 

 f the river which it cuts completely across. The posh 

 ! beds is here approximately as follows : 

 Upper quartzite, strike N 



W.. 



so' K.X.K. 





nearly 100 feet below Hie 

 ral river-bed, which is here quite shallow, appears at first 

 ; to be an old river channel. That this is not the case is 

 ed by the fact that on the right side (where it was open to 

 lination) it abuts against a hill, as is shown in the accom- 

 ing plan. The sh, flowing from this hill, 



the head of the cul-de-snc is 

 vated this 



o be found 

 >u ac that the river here flows across the 

 V:,J-Mun<io n... dofk.i strike of the lower beds and that, hav- 

 :> position of the ing cut the compact upper beds, it 

 found a soft bed of schist cutting across 

 its course and enclosed between two harder beds. The soft bed 

 now forms the soft clayey bottom of the canon, and though 

 decomposed still shows it! 



the fac 



Hie constr 



