360 



E. C. HARDER AND R. T. CHAMBERLIN 



formation ranges between 5 and 20 meters in thickness. In Morro 

 Agudo Peak it suddenly thickens to 100 meters (Fig. 6). Thirty- 

 odd kilometers away to the southwest, in the locality known as 

 Alegria, on the east slope of the Serra do Caraga, it has a thick- 

 ness of over 1,200 meters, which is probably its maximum. It is 

 not a case of steady increase, or decrease, in thickness between 

 areas some distance apart, for at the very eastern end of Alegria the 

 iron formation is comparatively thin, and the swelling from a few 



!«3(-i^ 



Fig. 6. — Morro Agudo, near Villa Rio Piracicaba. A peak of high-grade iron 

 ore which owes its form to the superior resistance of the hard, specular hematite of 

 which it is composed. 



score up to 1,200 meters is accomplished in the amazingly short 

 distance of about 3,700 meters along the strike (see Fig. 4). This 

 very remarkable thickening of the deposit in such a short distance 

 strongly suggests the conditions of delta deposition. If the layers of 

 iron formation represent the foreset beds laid down, shingle fashion, 

 on a delta front, the great total thickness of the successive layers 

 may be readily understood, and in this way some of the grave diffi- 

 culties which would otherwise be encountered in the development 



