OF TUE SERGIPE-ALAGOAS BASEST OF BRAZIL. 375 



{Ziaguncularia racemosa Gaoit. and Avicenma toinentosa Lin.) have reached matu- 

 rity, the mangues (swamps) are very nearly, if not quite, impenetrable, and tlic lapid- 

 ity witli wliicli old vegetation decays and young vegetation seizes uiion new and 

 reclaimed lands in the tropics, make them a moie powerful agent in the accumulation 

 of sediment and organic matter than aie the mangrove swamps of Florida. 



In its predominant features the belt of sandy lands and dunes does not diil'er in 

 any marked degree from that of any sandy coast. The sands drift with the winds, 

 and the conHgui-ation seen at one time is entirely obliterated a few weeks or a month 

 later. 



Kot infrequently these dunes are drivrn into the edges of the thick forests which 

 grow upon the adjacent topographic l)ell, but beyond this mai'gin tliey cannot pene- 

 trate far. The effect of the l)lown sand upon the vegetation in sueli cases is ver^^ 

 maiked. The flying grains soon bruise and kill the buds and tender leaves and ulti- 

 mately a peculiarly rounded, lobed and closely cropped appearance is given to the 

 windward margins of the forests. Although these dunes do not assume the propor- 

 tions in this part of the empire that they do in some of the more northern provinces,* 

 the entire coast of Sergipe and a large portion of that of Alaguas ai-e covei-ed by a 

 sandy belt which varies in width from five hundred feet to two or three miles. 



In some places the dunes predominate, the shifting sands often encroaching upon 

 and burying mangrove swamps and the xinderbrush of adjacent forests, whilr in 

 others they form broad, flat glades with a sparse and characteristic flora of cajus, 

 cacti, etc. From the Barra de Japaratuba to tlie mouth of the Kio Cotinguiba the 

 unbroken line of dunes thrown up Ijy the prevailing east winds has here am-sted tlie 

 drainage and turned it westward through the Kio Pomonga which Hows into the Co- 

 tinguiba just north of Araeaju.f To the south of the Cotinguiba these dunes often 

 assume extraordinary proportions.:!; 



The vegetation of the sandy belt is necessarily sparse at the best. Wherever 

 the sand is constantly shifting, as it is in the newer portions of the belt, vegetation 

 has no opportunity to take root. In those portions, however, in which, for any reason, 

 the sands assume more or less stability, certain drought-resisting forms of vegeta- 



* There lias been some speculation regarding the origin of Uiese viisl iicciimnliitions of sand along Uic IJra/.ilian 

 coast, anil especially about Cape St. Rorjue, M. ile Jonnes holding that they are brought lo these shores by the eqa- 

 torial current (see Ceaia, by Pompco de Souza, p. Ki). while Dr. Capanenia holds that they come from the Serra do 

 Araripe. Whatever may be the origin of the sands north of Parahyba, south of that point they are derived dirccllj' 

 from the rapid cutting away by the ocean of the soft tertiary beds. 



fSce also Relatorio da Commissao Hydraulica do Rio Siio Francisco, by W. Milnor Roberts, Rio de .Janeiro, 1880, 

 p.. I. 



t See Geology and Physical Geography of Brazil, by Cliaa. F. llarlt. p. 380. 



