230 The America)) Geologist. October, 1894 
huge bulk rendered them incapable of adapting themselves to 
new conditions, and a change of surroundings brought ex- 
tinction/'* 
The late Mr. S. V. Wood attempted to adduce an explana- 
tion of the break in the character of the faunas of the Creta- 
ceous and Tertiary periods in the European province from 
the geographic changes which then occurred. f He supposed 
that "the disappearance of the marine saurians was conse- 
quent upon that of the cestraciont fishes, the destruction of 
the latter having proceeded from the failure of the tetrabran- 
chiate cephalopods which supplied their food," these in turn 
owing their extinction "to the entire change which took place 
in the position of the shores at the close of the Cretaceous 
period.' 1 "This change.*" he thought, "was so complete that 
such of the shore-followers as were unable to adapt themselves 
to it succumbed, while the others that adapted themselves to 
the change altered their specific characters altogether."* The 
ammonites and other chambered cephalopods of the Mesozoic, 
he pointed out, we have reason to believe were, like the Nau- 
tilus, bpttom-feeders, and therefore shore-followers. Wood- 
ward^ supposed that the chambered cephalopods could not 
exist in depths exceeding 20 or 30 fathoms. The geographic 
change which Mr. Wood invoked was one from the littoral 
conditions of the Lias. Oolite and Cretaceous formations of 
England and northern France to the exclusion of the sea by 
the uplift and western extension of the European continent. 
so as to confine the waters of the Eocene nummulitic sea to a 
gulf such as that of Arabia or Persia. 
In North America, the completion of the peneplain was fol- 
lowed first by the submergence of the later Cretaceous, then 
by the reversed movements of the succeeding Eocene. In the 
Sierra Nevadas the faulted surface of the peneplain forms 
the even tops of the western slopes of the range; and in east- 
ern North America the peneplain has been differentially ele- 
*lbid. 
fOn the Form and Distribution of the Land-tracts during the Sec- 
ondary and Tertiary periods respectively; and <>n tin' effects upon Ani- 
mal I. if'' which great changes in Geographical Configuration have 
probably produced. Philosophical Magazine, fourth series, vol. win. 
inc.-.'. pp. 160-171, 269-282, :is->-:5<>:s. 
jlbul.. p. 384. 
SManual of Eollusca, second ed., 1871, pp. 184, 185. 
