I9I3.] REGION ABOUT NATAL, BRAZIL. 459 



94-103 Coarse, grayish, clayey sand. 



103-107 A brownish and grayish fine-grained, sandy clay which is black 

 when wet. 



" I might add that the well stopped here. There was more or 

 less water all the way down but none of a drinkable quality. The 

 name of the place where this well is located is ' Porto do Padre.' 

 Burgess told me that when the tide was high, the level of the water 

 in the well was low and when the tide was down low, the level of 

 the water in the well was up." 



The Sand-Dunes. 



The action of the sand-dunes on the northwest coast of Brazil is 

 of great importance. It is best studied along the coast for there 

 the waves sometimes cut into the banks and expose dunes of older 

 ages. Cross-bedding is the general form which it takes, distinctly 

 marked, and overlying the soft red sandstone series. The sand is 

 composed almost entirely of white quartz grains. It is blown back 

 from the coast and across the country. It forms long parallel hills 

 of yellowish color across the railroad south of Natal just north of 

 Pitimbu. Here it has been carried from Ponta Negra. This form 

 is common all along the coast in a belt about ten kilometers wide. 



An interesting work of the wind and sand was that in the valley 

 Extremoz. At the mouth of the valley, which is about two kilo- 

 meters wide, there is a bank of sand-dunes some thirty meters in 

 height, completely shutting in the basin. This bank must have ex- 

 isted some time, for a small lake, bordered by cocoa-palms, is 

 nestled in its crest. The valley back of it contains a series of long, 

 narrow freshwater lakes more or less connected end to end, but 

 distinctly separated on their sides by long parallel dunes running 

 lengthwise up the valley, standing almost as high as the surround- 



Otd river c^^A 

 Z.k. wid* 



Fig. II. Cross-section of the Valley of Extremoz, Rio Grande do Norte, show- 

 ing the system of parallel lakes between the sand-dunes which dam it up. 



