EXPOSURES ALONG THE CONDE D'EU RAILWAY 53 



1887-'88. Where the line crosses the ends of the mangrove swamps 

 northeast of Parahyba, great difficulty was experienced in building the 

 road on the soft mud on account of its yielding and slipping from be- 

 neath the load of earth that had to be heaped on it to form the roadbed. 

 As there are cuts in solid rock on both sides of one of the swamps, it was 

 supposed that the swamps had rock bottoms, and soundings were there- 

 fore made in the swamp to find the depth to the rock. These soundings 

 were successfully made with steel rods, and the mud was so soft that 

 two rods were lost by being dropped endwise in the mud ; they are said 

 to have sunk almost as promptly as if they had fallen in water. 



The accompanying profile shows the form of the rock bottoms of these 

 swamps. The greatest depth of the mud found on the line was 11.70 

 meters. It seems evident that the swamps here fill gullies formerly cut 

 in the gray Cretaceous limestone. Inasmuch as gullies can be cut at 

 such a place only when the surface is above waterlevel, it is inferred 

 that the land hereabouts formerly stood enough higher to allow water 

 to flow down through these channels. The present conditions have been 

 brought about by a depression of the old land surface that has carried 

 the ancient valleys beneath the sea, and the upper ends of these valleys 

 have been filled with silts and then overgrown with vegetation. The 

 depth of these channels shows that the amount of the land depression 

 was 12 meters at least ; but inasmuch as the soundings were made close 

 to- the Parahyba hills, it seems highly probable that farther west the 

 Parahyba estuary now covers the main channels and that they are much 

 deeper than 12 meters. 



The railway station at Parahyba is at the foot of the Cretaceous hills 

 on one side, while to the west and north stretch the mangrove swamps 

 of the Parahyba estuary. Three kilometers from the city of Parahyba 

 the track of the railway skirts a steep-sided hill on the left, with a man- 

 grove swamp on the right. The valleys along this portion of the road 

 are flat-bottomed. At Usina Sao Joao the flat valley floor of the Rio 

 Parahyba is about 4 kilometers wide. At kilometer 22 (from Parahyba) 

 there is a great flat freshwater marsh whose sides end as sharply against 

 the hills as if made by a body of water. The surface of this marsh is 

 about 5 meters above tidelevel (aneroid). An attempt was made to 

 build the railway across one of these marshes, but the roadbed sank 

 under the load made by the fill and the line had to be changed. This 

 fact is of interest in connection with the soundings made in the man- 

 grove swamps between Parahyba and Cabedello already mentioned. It 

 seems probable that the valley-cutting done during the period of eleva- 

 tion extended this far, and that we have here another silted-up narrow 

 valley. 



