26 bulletin: museum of comparative zoology. 



and on the notes of Steere.^ Gabb's opinion of the age of the deposits 

 he does not give correctly, but he quotes from Steere's notes facts that 

 appear to strengthen the idea of the Tertiary age of the beds. 



Dr. Oskar Boettger pubHshed in 1878 a paper upon the Pebas beds'^ 

 in which he describes several new species of fossils. He says the fossils 

 show the deposits to be of brackish-water origin laid down about the 

 mouth of a large stream, that there are no marine forms whatever, and 

 while he calls the beds early Tertiary he admits that inasmuch as the 

 fauna of the region is unknown, the age of the beds is really doubtful 

 (p. 503), — a view with which one must agree. 



Dr. "\V. H. Dall writes me privately : " As regards the Pebas fossils, 

 the}' are a unique and isolated group of which it is difficult to deter- 

 mine the age because all the characteristic forms are extinct and have no 

 obvious relatives. It may be as old as Eocene or as new as Pliocene, but 

 not, I think, younger."^ 



In 1879 Etheridge described a collection made by C B. Brown from 

 similar formations on the Solimoes and Javary.* These again are spoken 

 of as Tertiary, but no reasons are given for this classification. Most of 

 the species described by all these writers are new and the collections 

 therefore have but little diagnostic value, especially in the absence of 

 a knowledge of the existing fresh and brackish water faunas of that 

 region. 



Major Coutinho says that the formations at the mouth of the Huallaga 

 in Peru and at the head waters of the Japura, the Jurua, and the Purus 

 are the same as those of Marajo and along the coast to Piauhy.^ From 

 his description I take this formation to be what Hartt calls Tertiary and 

 Agassiz calls glacial sediments. But this sweeping correlation by 

 Coutinho must be regarded as extremely venturesome, and certainly with- 

 out a sufficient basis of facts. The table-topped hills of the Amazon 

 valley Hartt thought were Tertiary, but in these again no fossils were 

 found.® Hartt says in speaking of these formations that his " opinion 



1 C. F. Hartt. The Tertiary basin of the Maraiion. Amer. Journ. Sci., July 

 1872, CIV., p. 53-58. 



2 Die Tcrticirfauna von Pebas am oberen Maranon. Jahrb. d. K. K. Reichsan- 

 stalt, 1878, 28 Band, 3 Heft, p. 485-504. 



3 Private letter, April 26, 1901. 



* R. Etheridge. Notes on the Mollusca . . . from the Tertiary deposits of 

 Solimoes and Javary rivers, Brazil. Quar. Journ. Geol. Soc, 1870, XXXIV., p. 82-88. 



fi Bull, de la Soc. de Geographie. Paris, Oct. 1867, XIV., p. 321-334. 



6 C. F. Hartt. Recent explorations in the valley of the Amazonas. Ann. Rep. 

 Amer. Geog. Soc. N. Y. 1870-71, p. 246. 



