OF THE ^EU(in'E-ALA(;oAS UASI^' OF iji;a/il. 377 



idi'al tropical forests having an iimlorgrowtli \\ell-ni<i,h iin])('netrable and trees whose 

 enurnious trunks reath heights almost incredible. 



IV. Tlie semis, or the ixdeo-zoic region. — This type lies to the north and west of 

 tin- mesozoic region, and forms a well-dt'lincd, natuiai boundary Ixtween it and the 

 arclwean region which lies farther inland. In the province of Alagoas this border is 

 formed by the Scrra de Maraba, which, in its continuation to the south-west, is called 

 the Sena d'ltabaiana, anil still farther to the south Cajahyba. This entire range is 

 the monoclinal remains of the eroded landward margin of the beds here exposed. Tlic 

 rocks dip to the east and soutli-east at an angle of from fifteen to twenty degrees, 

 and underlie the cretaceous and other beds between the serra and the ocean. For 

 the most part these serras are covered with forests nearly to their summits. 



\. The irans-serra (w archcean region. — The topography of this region is an ex- 

 ceedingly varied one ; now hilly, now mountainous, and now spread out in gently 

 undulating plains. In some places it is notoriously sterile and is covered, for the most 

 part, with a sparse growth of stunted timber, while in otheis it is more fertile, and 

 produces a more vigorous forest. But little time was devoted to the geology of the 

 archsean region. 



THE SERGIl'E-ALAGOAS BASIN. 



It will be seen in the resume of what we know of the mesozoic geology of Brazil 

 that too little is known of the exact limits of the cretaceous basins along the noilli- 

 eastern coast of South America to permit a single one of them being clearly and 

 satisfactorily outlined. More work has been done on the Bahia basin than upon any 

 other one of the nuinl)cr, but of even this the limits arc not known. For the better 

 understanding of the region, it is deemed best, however, to give such facts as are 

 availabk' in rouglily outlining the Sergipe-Alagoas basin, before giving the details of 

 local geology. 



The Bahia beds being of lacustrine oi-igin, while those to the north are of marine 

 origin, it may safely be assumed that these two basins were independent of each 

 other at the time of the deposition of their beds. The most noith-uasterly point at 

 which the Bahia cretaceous is known to occur is neai' Cali'i in the province of Bahia, 

 and the most southerly point at which the marine cretaceous beds of the Sergipe-Ala- 

 goas basin have been observed, is at and about Estancia, in the province of Sergipe. 

 The southern margin oi' this basin nin>l, therefore, be to tin; mhiIIi ol' this place. The 

 rapids in the Rio Heal, known as Passagem das Tedras, suggests the possibility of 

 the red sandstones, which make the cataracts at Estancia, crossing the liio Heal at 

 Passagem. 



A. r. s. — VOL. .vvi. 2v. 



