460 ■ JENKINS— GEOLOGY OF THE [May 29, 



ing low plateau. These dunes are of old character, dirt}^ and cov- 

 ered with vegetation. In some places the lakes are round, but usu- 

 ally they are long and narrow. They are bordered by little or no 

 vegetation. Nearby a cocoa-palm grove may stand with its tiny 

 village. This condition continues for ten kilometers up the valley to 

 Logoa Agramara. Beyond there are a few meadows, dried-up ponds, 

 and sand-dunes which close up the valley farther on. Logoa Ex- 

 tremoz is a horseshoe shaped body of water beyond the sand-dunes, 

 situated at the junction of the two old river beds which go to form 

 the main valley. This lake has a tiny outlet which runs into a 

 marsh where it is dried up and sinks into the sand. The village of 

 Extremoz lies on its northern shore and the railroad passes in sight 

 of it. The general appearance of the lake as viewed from the car 

 window was that of a river, not a lake. Further examination 

 showed it to be a lake in an old river channel with two inlets, one at 

 each of the ends of the horseshoe. " The fish fauna of Lake Ex- 

 tremoz is made up of the usual fresh .water forms of the region 

 and, in addition, many typical salt water ones, such as Centropomus, 

 Mugil and Gcrras, showing that the lake has been connected with 

 the sea in recent years, though it is said to be cut ofif by sand hills at 

 the present time."'' These marine fishes are known to live for years 

 in the fresh water of the tropics but are not known to spawn there. 

 The habit of spawning in sea water is too great to be readily changed. 

 At Ceara-Mirim only fresh water forms were- found. At Papary 

 both fresh and salt water forms were found in the lake. The lake 

 in this case, although dammed at the mouth by sand, has at present 

 a direct connection with the sea. It is hard to see, in the case of 

 Logoa Extremoz, how fish can ever get out or how they have existed, 

 being away from the sea apparently for so many years. It is evi- 

 dent that at times of great floods the lake must connect with the 

 ocean. 



This damming in of fresh water is a common occurrence along 

 the coast but not always on such a large scale. Papary, which is 

 farther down the coast, is a river basin partly dammed in by dunes 

 at its mouth and made into a lake. 



^ E. C. Starks, "The Fishes of the Stanford Expedition to Brazil," p. 3. 

 Stanford University, March 17, 1913. 



