234 ORVILLE A. DERBY 
sedimentary table-lands of the Jaguaribe, Sao Francisco, Parahyba, 
coast rivers of Maranhao and Pardé, and Araguaya-Tocantins basins.* 
3. The oldest fossils known from this series present a preponder- 
ance of Cretaceous types, but with certain forms that standing alone 
would be referred to the Jurassic; the newest are of late Tertiary 
(Pliocene ?) types. The geological range is therefore from early( ?) 
Cretaceous to Pliocene, thus embracing both Mesozoic and Tertiary 
strata. 
4. Certain localities representing strata at or near the base of 
the series present faunas with a decidedly Tertiary aspect,? but with 
a small number of species that occur also in the typical Cretaceous 
beds. ‘The geological horizon of the beds at these localities is there- 
fore somewhat doubful, but for the present the preponderance of 
evidence seems in favor of a Cretaceous age. 
5. The typical fossiliferous Cretaceous beds are usually some- 
what disturbed, whereas the typical Tertiary ones are undisturbed, 
except probably by vertical movements; and, in the absence of other 
evidence, this circumstance has been used as a criterion for discrim- 
inating the Mesozoic and Tertiary members of the series, but it is 
obviously an unsafe one. ‘The assumption that the unconformability 
that doubtless exists is at the contact of the Cretaceous and Tertiary 
is a plausible one, but is unproven. ‘The evidence of conformability 
or unconformability is frequently very obscure, and thus becomes 
practically valueless in rapid reconnaissance work. 
Between the fossiliferous Cretaceous beds at the base of the series 
and the fossil leaf-bed near the top there is, in the Bahia section, 
t These indentations are represented schematically by dotted lines on the map on 
p. 222. Cretaceous fossils are known from these table-lands from southern Ceara, 
eastern Piauhy, and on the Sao Francisco below the great bend; and Permo-Carbon- 
iferous ones from the interior of Piauhy, andon the Maranhao. The great bay embra- 
cing a part of the Sao Francisco valley follows quite closely a larger and older Eo- 
Paleozoic one that over a great part of that region occurred between the Archean ( ?) 
shield of Bahia and Eastern Minas Geraes, and a second (not entirely detached from the 
first) in Goyaz. 
2 Compared by Professor G. D. Harris, (14 p. 18) with the fauna of the Eocene 
beds at Midway, Ala. ‘The resemblance is certainly a striking one, but, as above shown, 
its significance is greatly weakened by the recent discovery of a typical Cretaceous 
genus (Ammonites ?) in the immediate vicinity of one of the localities affording this 
doubtful fauna, and presumably from a bed belonging to the same geological horizon. 
