484 THE JOURNAL OF GEOLOGY. 



the most abundant and widespread of the Amazonian species, is 

 remarkable. 



Of the 38 species of the white decomposed cherts, also found 

 loose on the beach of Itaituba in small fragments, 17 have not 

 been found elsewhere at that place though four of them occur at 

 one or another of the other localities. The leading characteris- 

 tic of the chert fauna is the abundance of small lamellibranchs, 

 14 species, of which six have not been found in the other rocks 

 of Itaituba though three of them occur elsewhere, and of gastero- 

 pods, 13 species, of which seven occur also in the limestone and 

 one in the siliceous boulders. It is to be noted, however, that 

 the greater part of the fossils of these two groups found in the 

 limestone are from cherty nodules in the upper part, which leads 

 to the hypothesis that the white decomposed cherts may have 

 weathered out of the limestone or of some layer in immediate 

 connection with it. The two brachiopods, Spiriferina spinosa and 

 Chojietes amazonica, peculiar to the cherts, are exceedingly rare 

 forms. 



Stronger indications of a possibly independent fauna are 

 found in the few loose fragments of an impure argillaceous lime- 

 stone, from which five species are known, none of which have 

 been found in the purer limestone of Bom Jardim, though two 

 occur in the boulders and one, probably two, in the cherts. 

 These fragments possibly represent the rock from which the 

 boulders and cherts have weathered out, and presumably come 

 from above the limestone with a continuation of its fauna with 

 differences due to habitat. In short, all of the Itaituba material 

 indicates essentially the same horizon. 



The Maueassu limestone at Pedra do Barco and Frutal is 

 identical in aspect and character of the fossils with that of the 

 Tapajos at Itaituba. Of the 18 species known from Pedra do 

 Barco, two species of Productus, a Pleurotomaria, and an Enomphalus 

 have not been found at Itaituba. The limestone No. 3 at Lake 

 Cujubim has only one species, Productus cora, out of 1 1 not found 

 in that of Itaituba, although it occurs in the boulders and cherts. 

 This same Productus and another of the P. nebrascensis type 



