24 J. W . Dawson on Paleozoic Rhizocarps. 



" The third or Curua group consists almost exclusively of black 

 and red shales, passing at times into shaly sandstone. These beds 

 form low cliffs along the rivers Maecuru and Curua for a consider- 

 able distance, lying almost horizontal, except where disturbed by 

 eruptions of diorite. On the Trombetas the black shale forms 

 two short cliffs on the river-bank and the red shale is badly 

 exposed on a lake near by. At Erere these rocks are exposed in 

 the eastern part of the plain, and in the base of the serras, parti- 

 cularly that of Tajuri, the front of which is composed entirely of 

 these shales. The black shale forms the lowest bed, the thickness 

 of which, on the Curua, is estimated by Mr. Smith at 300 feet. 

 It is well laminated, almost slaty in structure, and in the lower 

 part contains numerous large calcareous and arenaceous concre- 

 tions. The first are bluish black in colour, have well-developed 

 cone-in-cone structure, and emit, when struck with a hammer, a 

 strong odour of petroleum." 



" The reddish shale lies above the black, having, more or less, 

 the same thickness. It is generally chocolate-coloured, mottled 

 with spots of a darker hue, and banded, parallel with the strati- 

 fication, with white, yellow or black. The rock consists of clay, 

 mixed with a considerable proportion of fine-divided mica and 

 sand, the last often forming independent layers a few inches 

 thick. The only fossils found in these shales were fucoids, of 

 the genus Spirophyton, and small fruit-like bodies, resembling 

 very much a flattened currant, consisting, apparently, of a thin 

 pellicle enclosing two to six small grains. The Spirophyton is 

 apparently identical with one of those described by Prof. Hall, 

 from the Hamilton group of New York. It occurs abundantly 

 in all the localities, in both the black and red shale, near the 

 junction of the two." 



" On the Curua and Maecuru the red shale, which is undoubt- 

 edly Devonian, is followed by beds of coarse sandstone which, 

 according to Mr. Smith, are at least fifty feet thick on the 

 Curua. This is followed by fossiliferous carboniferous beds. 

 The red shale is also overlaid by coarse sandstone, in the moun- 

 tains of Erere', but it is not certain that this sandstone is of the 

 same formation as that of the Curua." 



" As regards the extension of the Devonian series, it has been 

 recognized as far west as the river Uatuma, a small river 

 between the Trombetas and the Eio Negro. On the southern side 



