1879.] loJ [Derby. 



mentioned by Prof. Hartt, may belong to this series ; but as cherts arc com- 

 mon also in the Devonian and Carboniferous, it is impossible, in the absence 

 of specimens, to form a definite opinion respecting the age of those of the 

 Tocantins. 



The Devonian is best exposed on the northern side of the valley, where 

 it forms a broad belt, bordering the narrower Silurian belt, and disappears 

 under the Carboniferous deposits, to reappear farther south in the Erere 

 anticlinal. The beds of this age are variable in character, and may be di- 

 vided by differences in the rocks and fossils into three groups, which, for 

 convenience, may be named for the locality in which eacli was best studied, 

 the Maecuru, the Erere and the Curua group. It must be remembered, how- 

 ever, that all three of these groups are represented at each of the above lo- 

 calities. 



The first, or Maecuru group, consists of a few beds of coarse, white or 

 yellowish sandstone, which, on the Maecuru and Curua, have a thickness 

 of thirty feet. On both of these rivers this group is well exposed, with a 

 dip of about 5° S. S. W- The rock is hard in some layers, but very friable in 

 others, and is highly fossiliferous. On the Trombetas it is represented by 

 a bed of sandstone, so friable as to be almost a bank of sand, and at Erere 

 only a portion of the upper bed is exposed, and no fossils were found at 

 either of these localities. The fossils are impressions, colored and some- 

 what consolidated by oxide of iron ; they are beautifully preserved, and so 

 abundant and varied that, with a few hours' work, Ave made an enormous 

 collection, containing about seventy-five species. Trilobites are represented 

 by species of Homalonotus, Dalmania, Phacopsand Pi'ietus ; Gasteropods by 

 Bellerophon, Holopea and Platyceras ; Lamellibranchsby a large number of 

 speciesof the genera Modiomorptia, Limoptera, Edmondia, Grammysia and 

 others. The most interesting fossils are, however, the Brachiopods, which 

 have been carefully studied by Mr. Rathbun, who has described* twenty - 

 one species from the Maecuru, of winch thirteen were also found on the 

 Curua in equivalent beds, nine in the overlying beds of the Erere group, 

 and six in the lower and middle Devonian of New York. Of the species 

 common to this group and that of Erere, those that are abundant in one are 

 generally rare in the other, and this, with the numerous species which are 

 limited to each group, gives a special expression to the fauna of each, which 

 justified their separation. The most abundant and characteristic Brachi- 

 opods of the Maecuru group are Amphigenia elongata Hall, Spirijera duo- 

 denaria (?) Hall, Strophodonta perplana Hall, R7ii/nc7ioneUa dotis (?) Hall, 

 VituUna pusttdosa Hall, Streptorh ynehus Agassizii Hartt, and new species 

 of Ghonetes and OrtMs. The two first and the last new species were not met 

 with at Erere. It will be seen that these fossils indicate a close relationship 

 to the Corniferous group, which bears about the same stratigraphical 

 and pakeontological relation to the overlying Hamilton group, as does 

 the Maecuru group to that of Erere. These last two may, therefore, be 

 considered as the Brazilian equivalents of the North American formations. 



* Proceedings of the Boston Society of Natural History, Vol. XX, pp. II 39. 

 1878. 



rUOC. AMEIt. PHILOS. SOC. XVIII. 103. V. PRINTED MARCH 11, 1879. 



