AND RIO GRANDE DO NORTE, BRAZIL. 9 



brown sand, with no hard rocks at all. No fossils have ever been 

 found in this sandstone. The beds are at least 30 meters thick. 



Directly overlying the sandstone is a bed of hard, fine-grained 

 limestone which is usually of a grayish or yellowish color. It is 

 exposed in a continuous strip from near Aracaty to Natal and is 

 known to exist in several places between Natal and Parahyba. It is 

 not unlikely that this strip of limestone continues on uninterrupted 

 into the state of Pernambuco. As is shown on the accompanying 

 map, the escarpment of Apody, beginning in the vicinity of Uniao, 

 follows a general southwest direction until it reaches a point about 

 due west of Apody. There it swings sharply about and follows a 

 northeast direction to Passagem Funda. At Passagem Funda the 

 river Apody has cut squarely through the chapada and the east side 

 of the river is known as the Chapada do Sao Sebastiao while the 

 west side retains the name of Apody. In reality the two low plateaux 

 comprise a single physical feature. The escarpment of the Chapada 

 do Sao Sebastiao is a continuation of the scarp of the Chapada do 

 Apody. This former makes a detour to the south and then follows 

 a northeast direction to the village Rua da Palha. Here the same 

 thing has happened as was noted at Passagem Funda. The Rio 

 Upanema has cut through the Chapada do Sao Sebastiao and the 

 part of the serra which lies to the northeast of the river has become 

 known as the Serra or Chapada da Vacca Morta. The escarpment 

 of the Serra Vacca Morta trends a little to the northeast from Rua 

 da Palha as far as the northern margin of the Lagoa Piato, and 

 finally becomes lower and lower until about 6 kilometers east of the 

 lagoa, it merges with the low hills that make up the topography of 

 that region. The remarkable thing about this escarpment which 

 varies from 30 to 100 meters in height, is that it marks the contact 

 between the sandstone and the limestone. Everywhere along its en- 

 tire length the base of the escarpment is sandstone while the top is 

 limestone. The whole surfaces of the Chapadas of Apody, Sao 

 Sebastiao and Vacca Morta, are limestone. From the Lagoa Piato 

 to Natal the contact between the sandstone and limestone has been 

 only approximately located. It crosses the Rio Assii about 9 kilo- 

 meters north of the city of that name and continues in a general 

 easterly direction. Near the fazenda Sant'Antonio, 30 kilometers to 



