NEPHELDTE-KOCKS IN BEAZIL. 



463 



dyke, about 9 metres wide, which is of extreme interest (fig. 2). Owing 1 

 to decomposition, only detached fragments, still in situ, of perfectly 

 sound rock could be obtained, those near the margins being typical 

 phonolite, those near the centre foyaite equally typical. Another 

 case of the peripheral development of phonolite as a phase of 

 foyaite will be mentioned hereafter. 



Pig. 2.- — Section of Decomposed DyTce in cutting, Corrego do Quartet. 



9m. 



a. Decomposition-nodules of phonolite in decomposed dyke. 



b. Decomposition-nodules of foyaite in decomposed dyke. 



c. Decomposed micaceous conglomerate. 



Leaving the sandstone and conglomerate area at an elevation 

 of about 900 metres, which is presumably about its highest level, the 

 road, while following in general a nearly straight line for about 10 

 kilometres to the Cascata station, near the summit winds about for 

 a considerable space marked off by lateral valleys, in which the road 

 makes long and sharp bends to the eastward. The extreme points 

 of these bends are marked by the Pinhalzinho culvert, the tunnel 

 and viaduct, the intervening distances being 3 J and 2 kilometres. 

 In the U-shaped bends of Pinhalzinho and of the tunnel and viaduct, 

 where the road crossing the lateral valleys enters most into the 

 material of the mountain, nepheline-rocks alone are found, while 

 along the projecting portion of the lower space a dark- coloured 

 basic rock with prominent crystals of pyroxene is exposed in several 

 considerable cuttings. This is in general totally decomposed, showing 

 only rarely, in spots, stony nuclei of a mottled bluish and brownish 

 colour and heavily charged with white zeolites ; but in all cases the 

 outlines of the pyroxene-crystals are sufficiently well preserved to 

 serve for its ready identification. In one cutting only, between the 

 tunnel and Pinhalzinho, is the rock perfectly preserved. Two 

 types are here presented : one is a jet-black basalt, which, according 

 to a note kindly furnished me by Prof. Rosenbusch, is a leucitite ; 

 the other is a bluish-black tuffaceous rock containing pebbles up to 

 the size of the first of the leucitite, but as it also contains prominent 

 crystals of pyroxene, the two rocks cannot be distinguished in the 

 decomposed masses. The relations of these basic rocks to the 

 nepheline-series is shown in two cuttings between the tunnel and 

 the viaduct, represented in the annexed sketches (fig. 3). Both rocks 

 are much decomposed, but in spots are sufficiently preserved to make 

 their identification perfectly certain, while owing to the marked 

 difference in colour of the decomposition-products the line of contact 

 is remarkably sharp. I could not make out satisfactorily whether 

 the leucite-rock was originally a basalt or a tuff. The appearance 



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