410 THE CRETACEOUS AND TERTIARY GEOLOGT 



coast, namely, that they stand at different elevations, reduces itself to the suggestion 

 of a classification of geological formations by comparative elevations.* If all the beds 

 of the cretaceous both npon the coast and the interior Avere found to be perfectly 

 horizontal, with no evidences of faulting between, we might possibly be justified in 

 such an assumption. The position of the Sergii)e-Alag6as beds, however, shows that 

 this is not only not the case, but that in this basin, at least, the beds have a veiy 

 decided dip toward the ocean, while their inland margins rise to a height of from 400 

 to 500 metres or more where they overlie the paleozoic beds of the Itabaiaua. At 

 their inland margins they rise to the same elevation above a large number of expo- 

 sures of the same beds at tide level near the coast. If no connection had been ti'aced 

 out between these Sergipe localities we should be obliged, according to this hypsome- 

 tric classification, to separate those beds geologically. This suggestion must be 

 regarded, therefore, as a geological non seqiiitur. Mr. Dei-by assumes also that the 

 coastal cretaceous beds do not reach an elevation greater than 100 metres above tide. 

 This is erroneous. The serra of Itabaiaua is, according to Mouchez, from 700 to 800 

 metres above tide, and the cretaceous beds overlie the paleozoic beds of Itabaiana to 

 within 150 metres of its summit, which would make the elevation of the cretaceous 

 at this place above tide about GOO metres. 



Accoi'ding to the elevations along the Rio Slo Francisco, determined by Col. W. 

 Milnor Roberts, the river near Tacaratii and in the vicinity of the secondary beds 

 reported by Mr. Derby, is 320 metres above tide, and, according to him, the hills to 

 the north are about 303 metres above their bases,f or, say 620 metres above tide. 



The Ceara beds, according to Gardner, rise to an elevation of 600 metres above 

 tide, which would also indicate that, as far as elevations are concerned, there is no 

 impoitant difierenee between the interior and the highest of the coastal d(!posits. But 

 I lay no stiess upon this elevation of the coastal beds, for, to my mind, it is a matter 

 of but little importance, and I return to my original statement, that even if there 

 were very marked difterences of elevation, nothing could be deduced therefrom 

 iu regard to the relative geologic ages of the beds of the various localities. The ele- 

 vation of the Brazilian coast has not been an even one, and thei'e is certainly no rea- 

 son for supposing that it would be. The elevation or depression of coast lines, and 

 especially of lines as long as that from Rio de Janeiro to the mouth of the Amazon, 

 has seldom or never been known to be even or regular. It is true that the tertiary 

 beds along the Brazilian coast have a generally horizontal position, but this appear- 



* "It is (linicuU li> iulinit the contemponuieous ilepositioa of beds at sucli different elevations," Ai-chivos do 

 Museu Nacional, Vol. IV, p. 94. 



f Arc'hivos do Mus. Nac, 1879, Vol. IV, p. 91. 



