466 R. Rathbun— Geology of the Lower Amazonas. 
beds of the two series of the metamorphic deposits, but the evi- 
dence goes to prove that the older, or Laurentian; had been 
more or less disturbed and metamorphosed, before the deposi- 
tion of the newer, although the great general movement of up- 
heayal, that affected, and gave character to, the entire meta- 
morphic region of Brazil, was posterior to both. 
The formations above the metamorphic, so far observed in 
the Lower Amazonian valley, are the Upper Silurian, Devo- 
nian, Carboniferous, Cretaceous and Tertiary. The Upper Silu- 
rian immediately follows the metamorphic series, on the nort 
side of the valley, but has not yet been recognized to the south | 
of the Amazonas. On the Rios Trombetas, Curua and Mae- 
curt, where they were examined by Mr. Derby and his party, 
the rocks of this formation are exposed over an area of only a 
few miles in width, have an estimated thickness of about 1,000 
feet, and rest upon felsite and syenite; they are very gently in- 
clined, and consist mostly of thin-bedded, argillaceous and 
_ micaceous sandstones, with some massive beds of pure sand- 
stone. In the lower part of the series, on the Trombetas, are 
fossiliferous beds, containing in addition to other species, Ar- 
throphycus Harlani Hall, Lingula cuneata Con., Orthis hybrida 
Sow. and Bucania trilobata Con., which indicate an horizon cor- 
responding to the Medina Sandstone of the Niagara group of 
orth America. 
The Devonian rocks occupy a broader superficial area than 
entirely of black and yellowish shales, passing at times into 
2 shaly sandstones. The only recognizable fossils discov 
