19I3-] REGION ABOUT NATAL, BRAZIL. 445 



and are hard and siliceous. Other beds are softer and hmy, scattered 

 through with sand grains, while others are almost sandstones. At 

 the quarries, where the beds can best be studied, the more siliceous 

 parts are cast away and the limy portions put in the kiln. The 

 limestones usually show indications of fossils by small cavities and 

 poor casts of shells and plants, but actual remains of animals them- 

 selves were not found. Metasomatic replacement of the shells by 

 other minerals was not found to occur, although large irregular 

 cavities give place for the deposition of silica in the form of quartz 

 geodes. 



A slide of the limestone obtained near Itapasaroca was studied. 

 The following minerals in irregular grains were found in it : quartz 

 orthoclase, microcline, and mica (biotite and also probably musco- 

 vite). The main part of the rock is a fine-grained carbonate con- 

 taining both calcite and dolomite. Chemical tests showed some 

 portions of the rock to be more dolomitic than others. It may be 

 called a magnesian limestone. 



Detailed Description. — The following are the principal localities 

 studied where the limestone series is exposed in cuts : 



1. Itapasaroca, — railway cut at kilometer 45, exposing limestone 

 beds containing fossil casts of shells and plants. 



2. Ceara-Mirim, — a quarry near kilometer 35. Limestone is ex- 

 posed but there are no fossils. 



3. Jacoca, — four kilometers southwest of Ceara-Mirim two quar- 

 ries expose fossiliferous limestone beds. Here the line of the uncon- 

 formable contact with the red-sandstones may be definitely traced. 



4. Masaranduba, — fifteen kilometers north of Macahyba. A 

 quarry is on the bank of one of the inlets to Lagoa Extremoz. There 

 were only bare traces of fossils in the limestone beds. 



5. Desterro, — seven kilometers north of Macahyba. A quarry in 

 sandy fossiliferous limestone. 



6. Alvoredo, — exposure on the bank of Rio Potengy, three kilo- 

 meters north of Macahyba. Here limestone, with faint traces of 

 fossils, lies directly on top of the granite, also exposed in the stream. 



All expose practically horizontal beds, which have the general 

 tendency to dip towards the ocean to the southeast. These lime- 



