68 J. C. BRANNER GEOLOGY OF NORTHEAST COAST OF BRAZIL 



West and northwest of ILha the Tertiary hills are about half a kilo- 

 meter from the railway station. Half a kilometer beyond Ilha the hills 

 are about 100 meters northwest of the railway. Where quarries have 

 been opened in these hills the exposures are quite red. Just west of Ilha 

 two streams, the Rios Gurjahu and Pirapama, join each other, and the 

 hills on the northwest side of the road follow up the left side of the 

 Gurjahu and appear again on the point of land between these two 

 streams. At Cabo (kilometer 31.5 ; elevation, 13.3 meters) the hills south 

 of the railway are within a stone's throw of the station. At this place 

 the railway leaves the low flat coastal plain and enters the hills. In the 

 outskirts of the city of Cabo there are several cuts, all of them exposing 

 red, yellow, and mottled earth resembling the highly colored Tertiary 

 beds. The rocks, however, are not Tertiary, but crystalline rocks decom- 

 posed in place. The hills about Cabo and west of there as far as Boa 

 Sorte are from 50 to 75 meters above the drainage. The region is thus 

 a hilly but not a mountainous one. 



BOCK DECOMPOSITION 



The granites and gneisses along the railway are usually deeply de- 

 composed, having red, yellow, white, brown, purple, or mottled residu- 

 ary clays exposed in the railway cuts, and exfoliated boulders of decom- 

 position or rounded bare bosses over the surface of the ground. The 

 depth of the decomposition of the rocks is fairly well shown in a number 

 of the deep cuts along the line of the railway, but it is a notable fact 

 that in many even of the deepest of these cuts the total depth of the 

 decomposition is not shown. A rather remarkable thing about the deep 

 cuts in the residuary earth is that many of the faces exposed in such cuts 

 are nearly vertical, and yet they have stood for many years without falling. 

 The following are some of the deeper cuts where decomposition is well 

 exposed : 



One kilometer south of Limoeiro station a cut 14 meters deep has the 

 rock decomposed to the level of the railway track. On the divide east 

 of Palmares cuts 12 meters deep expose red and yellow residuary earth 

 crossed by quartz veins. 



At Palmares station (kilometer 124; elevation, 120 meters) there is a 

 cut 6 or 7 meters deep in decomposed crystalline rock. The residuary 

 cla}^ is red and purple and is crossed by the broken quartz veins. The 

 earth of the upper part of the cut is apparently handled material de- 

 rived from the same decomposed rock, for the quartz that appears as 

 vertical veins in the lower part of the exposure is scattered in subangular 

 fragments along horizontal bands through the upper part of the earth 

 exposed in the cut. 



