OF THE SER«4IPE-ALAG0AS BASIN OF BRAZIL. 381 



and Sto. Ainaro to the sea. No attempt is made to repieseiit ivlative thicknesses 

 accurately, for no measurements have been made that will render this possible. 





Section across the Sergipe-Alagoas basin. 



Beginning at the base of the section, M represents the crystalline rocks of the 

 arclmean, here composed of beautiful greenish gneisses containing amethysts and yel- 

 low mica. At the point of contact the surface is uneven but hard and rounded as if 

 water worn, and the conglomerates of the lowest of the paleozoic beds lie uncon- 

 formably upon it. The gneisses at this place dip to the north-west though much 

 crumpled in places. The same locks when exposed away from the line of contact ai*e 

 soft and deeply decayed. 



The lowest bed of K is a coarse and very hard conglomerate made up lai-gely of 

 fragments from the underlying gneiss. The next bed above is of coarse sand and 

 pebbles, false iiedded, followed by sandstone of varying degrees of coarseness. The 

 pebbles in this bed are of all sizes np to that of one's fist, and vary in color from the 

 white of milky quartz to the green of the underlying gneiss from which the latter are 

 ajjparently derived. Xext follow very hard sandstones with ripple marks, then fine, 

 fine-grained sandstone. This is succeeded by tine-grained micaceous slaty rock 

 with ripple marks, then very hard conglomerate followed by solid fine-grained slate, 

 and coarse sandstone with micaceous bands. 



These beds are all exceedingly hard, the sandstones being usually in the form of 

 jointed and strongly false-bedded glassy quartzites. They have a uniform dip of from 

 lo"" to 20- to the south-east. 



Of the thickness or importance of the rocks between the beds ju.st mentioned and 

 the next observed, nothing is known. On the sides of the liills immediately east of 

 Itabaiana a .series of slates, .shales and sandstones were seen, but it was too imperfectly 

 exposed to admit of a complete section being made, or of connecting such a section 

 directly with that in the Rio Sergipc gap. On the part of the mountain east of the 

 river the rocks dip south and south-east. The next overlying beds seen arc limestones 

 exposed on the stream between Itabaidna and Seira Comprida. Where they were 

 examined they are considerably distiu'bed, very compact, and traversed by .small veins 

 of white quartz. In general appearance these rocks resemble the mountain limestones 

 of England, but no fossils were found in them. 



