0. A. Derhy — Magnetite Ore Districts in Brazil. 315 



apatite. In an opening close to the supposed contact the jacupi- 

 rangite (profoundly decomposed) is of much coarser texture 

 than is ordinarily the case, with large perfect crystals and crys- 

 talline groups of magnetite, an unusual amount of apatite, and 

 large flakes of hydrated biotite with perfect crystalline out- 

 lines that appear to form a primary constituent of the rock. 

 The limestone in the neighborhood of the contact contains 

 orthite, which is found abundantly in beautiful microscopic 

 crystals in the sands of the streams flowing from the limestone 

 ridge, but has not been met with elsewhere. At the margin 

 of the- area a small isolated hill of Cambrian (?) schists and 

 eruptive rocks of a different type is partially surrounded by 

 jacupirangite, but the contact zone is occupied by swamps. In 

 the saw-mill pit small dykes of foyaite (nepheline-syenite) are 

 seen cutting the jacupirangite which, near the contact, shows 

 large mica flakes as at the supposed limestone contact. 



At Ipanema an ore pit in what is presumed to be decom- 

 posed jacupirangite shows clearly the eruptive origin of the 

 iron-bearing rock at this place, since it presents a well charac- 

 terized dyke margin against decomposed schist and, for a dis- 

 tance of a few meters from this margin, a well defined breccia 

















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character due to the inclusion of irregular angular fragments of 

 the schist, as shown in the annexed reproduction of a photo- 

 graph, in which the lighter colored schist fragments are seen 

 scattered helter-skelter in the dark iron-bearing rock. The 



