R. Rathhun — Oeologtj of the Lower Amazonas. 467 



were Syiroiyliytons, apparently belonging to the same species as 

 those described from the Hamilton group of New York. 



The Devonian rocks in the Erere region have suffered greatly 

 by denudation, and are much dislocated and divided by trap 

 dykes, making their study very difficult. Beds apparently of 

 Devonian age have been found as far west as the Kio Uatuma, 

 and, to the south of the Amazonas, on the Tapajos and Xingu. 



Of all the Paleozoic deposits of the Amazonian valley, the 

 Carboniferous is exposed over the largest area, but, at the same 

 time, presents the greatest difficulties to study. Being com- 

 posed for the most part of soft rocks, it has been much denuded 

 only widely-separated exposures remaining, of which it is 

 difficult to determine the correlation of the several beds. It is, 

 therefore, also impossible to estimate with certainty the thick- 

 ness of the series, which probably exceeds 1,800 feet. The 

 rocks are soft sandstones, shales and limestones, of which the 

 latter, though having the least thickness, are the most important, 

 from their being the best preserved and the richest in fossil 

 remains. The fossiliferous beds, originally studied by Prof. 

 Hartt and Mr. Derby on the Tapajos, were traced to the north 

 of the Amazonas, on the Rios Maecurii, Curua, etc. The differ- 

 ent exposures, however, appear to represent about the same 

 limited horizon, charactei'ized by identical fossils. 



The region over which the Carboniferous has been actually 

 observed, is defined by Mr. Derby as follows : On the south 

 side of the valley, it reaches up the Tapajos, to near the base of 

 the rapids ; westward it extends to, or beyond, the Rio Mauhe- 

 assii, situated midway between the Tapajos and Madeira, and 

 eastward to, or beyond, the Xingii. To the north of the Amazo- 

 nas, it stretches some distance northward of the region of Alen- 

 quer, partially covering up the Devonian between Erere and 

 the Maecurii locality, and has been found to the west, on the 

 Rio Uatuma, and to the east, on the Rio Jauary near Prainha. 

 There can be no doubt but that the Carboniferous really ex- 

 tends much farther west, and eastward, to near the Atlantic. 

 From what has been said before, however, it will be under- 

 stood that this formation is not exposed over the entire region 

 above defined, although at one time it must have been con- 

 tinuous there. It was observed on the principal rivers men- 

 tioned, generally in the vicinity of the lower falls or rapids, 

 and also at many intermediate localities, but is mostly covered 

 up by more recent formations, or by dense forest growths, and 

 over large tracts has been completely swept away. Notwith- 

 standing the fact that the fossils of this group indicate an hori- 

 zon, equivalent to the Coal Measures of North America, no 

 seams of coal have yet been found on the Amazonas. The 

 beds lie as a rule nearly horizuntal. 



