394 THE CltETACEOUS AND TERTIARY GEOLOGY 



THE AGE AND CORRELATION OF THE MESOZOIC BRAZILIAN ROCKS. 



Although the mesozoic beds of the region under discussion are here spoken of as 

 cretaceous, the writer is aware of certain conflicting evidence in regard to their age, 

 which should not be overlooked. 



Prior to the study of the cretaceous fossils of Brazil by Dr. White, the age assigned 

 to the beds from which these fossils weie derived was more or less unsatisfactory. 



Although undoubted paleozoic deposits occur in many places in Brazil, no fossilif- 

 erous strata have as yet been discovered immediately beneath the cretaceous, while the 

 overlying beds, referred to the tertiary, have never yielded any fossils, and have been so 

 referred solely on account of their relation to the strata underlying them. It is plain, 

 therefore, that the determination of the age of these rocks must be based entirely upon 

 internal evidence, a determination which, on account, of the incompleteness of the col- 

 lections or the want of study, has alwaj's been more or less unsatisfactory up to the 

 publication in 1SS8 of Dr. White's important '" Contributions to the Paleontology of 

 Brazil." 



Prof. Hartt, in his " Geology and Physical Geography of Brazil," p. 385, says that 

 when, in 1869, the cephalopods collected by him at Maroim were shown to Prof. Alpheus 

 H}alt, he was at once struck by their Jurassic aspect, although in the description of 

 these fossils, which is published at length in Prof. Hartt's book (oj) cit., pp. S85-393), 

 nothing is .said upon this subject, while they are all said to have come from " the creta- 

 ceous beds of Maroim." 



Prof. Hartt says {op. cit., p. 393) that the limestone about Maroim is undoubtedly 

 upper cretaceous, though he does not tell us upon what evidence this opinion is based. 



The Brazilian cephalopods described by Prof. Alpheus Hyatt in Hartt's " Geology " 

 had been collected by Prof. Hartt from what he considered undoubted cretaceous rocks. 

 Some of these fossils, however, were of decided Jurassic affinities, and both their strati- 

 graphic position and peculiar state of preservation warranted Prof. Hyatt in endeavor- 

 ing to account for their occurrence at such a horizon. Prof Hartt felt confident that the 

 Sergipe rocks were cretaceous ; the fossils were evidently much worn, and had a decided 

 Jurassic aspect. Prof. Hyatt therefore suggests* that these cephalopods may have been 

 eroded from beds at a lower geologic horizon (the Jurassic) and transported to and depos- 

 ited in the cretaceous. The suggestion is a natural one for a person unacquainted with 

 the peculiar circumstances under which these fo.ssils occur, but it is only necessary to 

 say here that a knowledge of these circumstances does away with .the necessity of this 

 supposition. The fossils were taken from their original beds, and there is no reason for 



*Proc. Boston Soc. Nut. Hist., Vol. XVII, p. 370. 



