AN OLDER CATINGA LIMESTONE 199 



Sao Francisco Railway, where one always has the railway elevations near 

 at hand. That particular deposit is here described in some detail because 

 it may be taken as a type of the older deposits of the kind in the region, 

 and because its character is suggestive of what may occur under favorable 

 circumstances in other parts of the world. 



Passing northward along the line of the railway, the Catinga limestone 

 first appears about 8 kilometers north of Angico, in the gullies east of the 

 railway at kilometer 391 and at an altitude of 489 meters above tide. 

 The rock here is quite soft and marly, and forms a layer less than a foot 

 thick. The overlying and accompanying soil has a peculiar snuff color, 

 and beneath the limestone the rocks are granites, gneisses, and crystalline 

 schists in place. 



At kilometer 394 + 400 and 450 meters are some pits dng about 5 feet 

 deep on the east side of the railway. These pits penetrate soft tufaceous 

 limestones that show horizontal bedding and contain grains of quartz 

 sand. At kilometer 394 -{- 5Q0 meters a pit on the west side of the road 

 shows tlie soft limestone horizontally bedded, and imbedded in the lime 

 rock are water-worn boulders of quartzite, along with quartz sand and 

 fragments of feldspar. In another pit on the west side of the track the 

 limestone contains much disintegrated granite. Here was found im- 

 bedded in the soft lime rock, and about oO centimeters below the surface 

 of the ground, the large living land shell, BuUnius oblongus Mull. This 

 was the first fossil shell found in the Catinga limestone, though many 

 were found later. 



At kilometer 395 + 10 the railway passes over the channel of Rio 

 Mossoro. There was no water in the channel at the time when these 

 studies were made, and the rocks exposed are all crystalline. On both 

 sides, however, the limestone overlies the crystalline rocks. From this 

 place northward to the top of the watershed at kilometer 400 the hard 

 lumps of limestone thrown from the ditches beside the track show that 

 rock is everywhere near the surface, and that it generally contains some 

 sand and water-worn pebbles. Near the top of this grade a ditch had to be 

 dug deeper than usual in order to drain a small lake bed (Lagoa de 

 Mulungu), through which the railway passes, and the limestone taken 

 from this trench is harder than that nearer the surface, while some of the 

 water-worn boulders of quartz are as mucli as 15 centimeters in diameter, 

 and smaller ones are more abundant. Some of these boulders are of 

 granite and some are of schist. This ditch, the Vallo do Mulungu, is 

 1,300 meters long and extends past kilometer 399, furnishing a fairly 

 good exposure of the limestone. The rocks are rather unevenly horizon- 



