204 Annals of the Carnegie Museum. 



may not be warranted. It seems to the writer, however, that a few 

 salient features are indicated by the observations of structure in the 

 gneiss, schist, and quartzite, in the area shown on the northern sheet 

 of the accompanying map (Plate IV). Sharp anticlines and synclines 

 seem to be shown by the reversals in dip in a number of places. In a 

 few places monoclinal structures, notably at the Lavras dam site, 

 presumably are the result of faulting. In addition to these minor 

 structures, a major feature seems to be indicated by the change in 

 the mean direction of the strike. From ^ general east-west course in 

 the zone from near Soledade westward to Assare, it swings to a north- 

 east-southwest direction in the region north of this zone and also 

 between Assare and Arneiroz, and to a north-south direction in the 

 zone thence northward to Cratheus. The direction of strike along the 

 railway between Iguatti and Quixada, although varying considerably, 

 seems as a whole to conform to this general plan. The direction of 

 trend of the planes of foliation seems to be such as might be produced 

 by compressive forces acting from the south and the w'est. 



This hypothesis is advanced with due appreciation of the fact that 

 it is based on incomplete data as to structure throughout the area sup- 

 posed to be involved in such compression; but the topographic evi- 

 dence, so far as the mountain ranges have been mapped, seems to 

 corroborate the evidence furnished by observations of the strike. 

 Attention is called to the east-west trend of the range composed of 

 the serras of V^ital, Santa Catharina, and Melado; to the northeast- 

 southwest trend of Serra da Barriguda and associated ranges, and 

 Serra do Camara and its northward extensions, and to the north- 

 south trend of Serra dos Oros and the range or series of hills extending 

 north from it. Farther west, topographic evidence of the same major 

 structure seems also to be indicated by the nearly east-west trend of 

 Serra de Sao Pedro, by the northeast-southwest trend of Serra dos 

 Bastioes and Serra de Arneiroz, and by the more nearly north-south 

 trend of Serra do Flamengo and Serra do Maia. Somewhat similar 

 general structure for this region was implied by Crandall,^^ who 

 observed that the granitic ranges nearly all trend northeast-southwest, 

 the only notable exception being Serra do Pereiro, which trends more 

 nearly north-south. 



So far as was observed, the foliation planes do not tend to wrap 

 themselves around the granitic masses. In some areas comparatively 



22 Publ. No. 4 of the Inspectoria, p. 27. 



i 



