1879.] -Ibd [Derby. 



pally of flesh-colored feldspar, with a small mixture of hornblende and 

 small scattered spots of a green mineral in decomposition. Quartz is en- 

 tirely lacking. 



The rocks of the second mctamorphic series are well exposed in the first 

 rapids of the Tocantins, where they were examined as far as the Cachoeira 

 de Guariba, by Prof. Hartt in 1870. The following notes are taken from 

 his manuscripts. Ascending the Tocantins, the river is at first margined 

 by bluffs of Tertiary sands and clays which, as the rapids are approached, 

 recede from the river and the metamorphic rocks begin to appear. The 

 first exposure of these last met with, is "A granular cpiartzite, very hard and 

 with a saccharine fracture, the rock being much traversed by quartz veins. 

 The stratification is veiy obscure and the rock appears to have a sort of 

 slaty structure. In some places it is very compact, bluish and cherty, and 

 is so cut up by veinlets as to appear honey-combed on decomposition. Next 

 appears, at the Ponta do Noberto, a talcose rock, badly decomposed, but 

 appearing to have an easterly dip. Above this is a bed of compact reddish 

 quartzite. From the Praia dos Mortos there extends a long line of similar 

 rocks, with an easterly dip. At Jequirapua, I found the following section, 

 given in ascending order : 



1 . Shaly sandstone. 



2. Compact white sandstone, rather fine grained, the grain being clear. 

 It weathers brownish, and is traversed by quartz veins. 



3. A thin band of purple shale, stratification obscured by faults and ob- 

 lique slips. 



4. Heavy band of ferruginous shale, much decomposed. 



5. Bed of very compact bluish, whitish and reddish mottled quartzites. 



6. Red shale much traversed by little veins. Just below Alcobaca, I 

 observed quartzite with a north-east dip. At Alcobaca are heavy beds of 

 bluish quartzite, very hard aud presenting surfaces polished by the river." 



Compact quartzites were observed at various points above Alcobaca, in 

 one place with the strike corresponding with the direction of the river, 

 forming long rocky islands or lines of rock. The dip is well marked, be- 

 ing a few degrees north of east, the angle being about 40°. 



"Just below the Cachoeira (rapid) de Tapanhuaquara are green schis- 

 tose rocks, dipping eastward, and much diorite. In the schists I found 

 amianthus and serpentine. The rocks that choke up the river and form 

 the rapids are, as far as I could determine, a series of gray quartzites, in- 

 terstratified with thin beds of finely laminated shale. The upper end of 

 the high wooded Una das Pacas is composed of a mass of hard, vitreous- 

 looking, bluish or reddish quartzite, much traversed by little quartz veins. 

 On the left bank opposite are ledges and skerries of a slaty rock, with a 

 strong easterly dip. The islets of Janauquara are bare masses of a hard 

 cherty rock, whose relations to the other rocks I did not determine. 



"At Porta de Braga, a bluff projection on the left bank of the river, the 

 shore is encumbered by very large masses of iron ore, in part a mammillary 

 hematite. The rocks of the vicinity, consisting of quartzites and sand- 



