EXPOSURES ALONG GREAT WESTERN RAILWAY 87 



in the particolored Tertiary beds. These beds were examined for fossils, 

 but none were found. 



It should be mentioned in this connection that the reservoir at Dois 

 Irmaos, northwest of the city of Pernambuco, is on one of these Tertiary 

 hills, and that the summit of that particular hill has an elevation of 81 

 meters above tide. 



The cuts at and near Macacos have given the railway company much 

 trouble on account of the landslips that often occur in them during the 

 rainy seasons. The white layers are especially liable to cause these land- 

 slides. This is due to the fact that these white beds are mostty kaolin 

 deposited from the decomposed feldspars of the underlying crystalline 

 rocks. When these kaolins become wet they are exceedingly slippery. 



About half a kilometer beyond Macacos, where erosion has cut deeply 

 into the Tertiary sediments, the underlying granite is exposed in patches. 

 One kilometer beyond Macacos the granite (or gneiss) is exposed by the 

 railwa}^ track. 



The exposures of the old crystalline rocks show that their upper sur- 

 face is quite uneven, for the Tertiary sediments are exposed in many 

 places at lower as well as at higher elevations than the granites. 



At Camaragibe (kilometer 18.3; elevation, 35.24 meters), north of 

 the track and half a kilometer beyond that station, granite is exposed. 

 The Tertiary continues a little beyond this point, though it is more or 

 less patchy north of Camaragibe. 



The railway enters the valley of Rio Capibaribe at Camaragibe and 

 follows it up to Pao d'Alho. It is worthy of note that the line of the 

 railway, instead of following up the valley of Rio Capibaribe, leaves 

 the plain through which that stream enters the ocean, passes through 

 expensive cuts over the watershed at Macacos (elevation, 47.24 meters), 

 and descends again to the Capibaribe at Camaragibe (elevation, 35 

 meters). Upon inquiring the reason for this, I was told that the railway 

 was not built through the gulch past Apipucos on account of the soft 

 and spongy nature of the soil that fills the narrow valley. 



A kilometer below Sao Lourenco there are terraces along both the 

 banks of Rio Capibaribe at an elevation of about 10 meters above mean 

 waterlevel. These terraces are visible for some 3 or 4 kilometers along 

 the river. At many places the rocks are well exposed in the bed of this 

 stream. 



From Sao Lourenco upstream for several kilometers the rocks ex- 

 posed in the stream bed are gneisses. At Sao Lourenco the gneiss is cut 

 by a granite (or pegmatite) dike. 



About 200 meters beyond the station at Tiuma the railway cuts gneiss 

 that is decayed to a depth of nearly 20 meters. Here and there through 



