224 ORVILLE A. DERBY 
unhesitatingly have referred to the former. Such perplexities are 
not unknown in other regions where the difficulties of geological 
study are far less than in Brazil, and where the number of geological 
students to set about unraveling them is far greater. They are of 
great importance when attempts at areal geology are to be made, 
but for the region in question they may for the present be put aside. 
The really important questions for the moment are: Is the reputed 
division into an upper and a lower series a real one; and, if so, what 
part, if any, of the latter belongs to the Cretaceous ? 
Dr. Branner apparently does not put in doubt an affirmative 
answer to the first of these questions, and this, therefore, can be 
summarily put aside. In regard to the second he expresses serious 
doubts, which, however, seem to have varied from time to time; 
and this makes it desirable to discuss the question, locality by locality. 
The fossiliferous beds of all the numerous Sergipe localities exam- 
ined by him are unhesitatingly set down by Branner as Cretaceous, 
and the overlying non-fossiliferous ones are referred to the Tertiary, 
apparently on the same stratigraphical and topographical criteria 
that were used by Hartt and others. Some of the species are admitted 
by him to present a decidedly Jurassic aspect, and on referring to 
Dr. White’s memoir we find that their number (nine) is somewhat 
in excess of that (seven) cited from the Pernambuco beds to establish 
their Tertiary age. Curiously enough, the beds containing the 
greater number of these species of Jurassic aspect are the same that 
carry the greater number of the species common to the Pernambuco 
and Pard beds which Branner would refer to the Tertiary, and the 
most decided Jurassic form of all (an Ammonite) is from a bed 
that is referred to the top rather than to the bottom of the series which 
is given as presenting a considerable vertical range. The most 
characteristic Cretaceous forms are the Ammonites, represented by 
fourteen species, of which only three occur in the three localities 
most abundant in other mollusks. If, therefore, by the chances of 
collection, only these localities had been examined, and if these few 
Ammonites had been overlooked, a doubt regarding the Sergipe 
basin as between Jurassic and Cretaceous might have been raised 
on the same ground as that raised between Cretaceous and Tertiary 
for the Pernambuco and Para basins. Some of the other localities, 
