174 Foraminiferal Origin^ Etc — Hill. 
Cornish and Limerick, S. 22° E. ; in Portland, at two localities, 
S. 23° E., and S. 3° E. , and in Cape Elizabeth township, 
S. 8° W., and S. 12° and 22° E. On Mt. Abraham he notes 
striation S. 59° E., and on the top of Mt. Pleasant, in Denmark, 
S. 41° W., but on the west side of Mt. Pleasant, near its top, S. 
31° to 33° E. 
(to be continued.) 
THE FORAMINIFERAL ORIGIN OF CERTAIN CRETACEOUS 
LIMESTONES AND THE SEQUENCE OF SEDIMENTS 
IN NORTH AMERICAN CRETACEOUS. 
By Roeekt T. Hill. 
The writer has recently published a resume ' of the occur- 
rence of chalk in the North American Cretaceous, and shown 
that in the United States there were two distinct and long 
continued epochs of subsidence within that period, each be- 
ginning with arenaceous littorals and insensibly gradating 
from them, through arenaceous clay shales, clay shales and 
calcareous shales, into culminating chalk deposits of great 
thickness and extent. 
In the uppermost of these Cretaceous formations, (the Meek 
and Hay den section and its equivalents) the chalky rocks of 
the Niobrara horizon have frequently been noted in Kansas 
and elsewhere. Its continuation and uniformity through 
Texas and into the southw^est corner of Arkansas is so appar- 
ent that it need not be discussed here further than to remark 
that it presents nearly everywhere a uniformity of foramin- 
iferal structure. The sediments of the lower Cretaceous have 
been less understood, however. Although strata of pure un- 
changed chalk are occasionally found in them, sometimes 
accompanied by nodules of the most perfect flints, the greater 
part of these limestones, through the changes of time are too 
hard to be longer called of chalky texture. Nevertheless, as 
we shall show, they are of chalky origin. 
In order to fully determine the origin of these limestones 
the writer has directed a series of experiments in the geologi- 
cal laboratory of the University of Texas. Among these was 
the making of a series of thin sections and microscopical 
examinations of the rocks of all the horizons. None of the 
lower Cretaceous limestones except a few feet of the basal 
^ Vol. II of the Report of the State Geologist of Arkansas, 1888. 
