140 The American GeologtH. September, 1894 
est of its family that has come to light, the longest previously 
known scarcely exceeding one-half of this size. Dr. (lark is, 
however, in possession of one or two cladodont teeth too large 
to correspond with the dimensions of the smaller specimens, 
which have for some time indicated to him the existence of 
larger forms hitherto unknown, the first of which isdescrihed 
in this note. 
These researches and discoveries have estahlished the exis- 
tence of an abundant selachian fauna in the Cleveland shale, 
with the general form of which we are now much better 
acquainted than Ave are with those later ones from the Car- 
boniferous limestone whose spines and teeth have long been 
abundant in our museums, but of which themselves we have 
yet but the merest glimpse in one or two ill preserved speci- 
mens in European collections. 
THE NIOBRARA CHALK. 
By Samuel Calvin, Iowa City. Iowa. 
CONTENTS. 
Page. 
Areal Distribution 141 
Physical Characteristics 142 
Stratigraphical and Bathymetrical Relations. . 142 
Characters of the deposits in different localities compared 14; 
Paleontology of the Chalk 14b 
Hesitancy of American geologists to recognize the Niobrara 
deposits as Chalk 147 
What is Chalk? i 4 v 
Some References to Literature in which either the Chalky 
Character or Eoraminiferal Origin of the Niobrara depos- 
its is recognized 1 4c) 
Composition of the Niobrara Chalk in the Sioux river region 153 
The Micro-paleontology of the Chalk [54 
The Foraminifera, with Observations on their Distribution 155 
Probable cause of the differences observed 1 jq 
Comparison with English Chalk ; 160 
It was my original purpose to take for the subject of this 
discourse some geological problems in northeastern Iowa, but 
certain circumstances made it seem more desirable to transfer 
attention to the northwestern part of the state and discuss the 
more striking features of the Niobrara chalk. 
*Vice-presiden-tial address before the section of Geology ami Geogra- 
phy, American Association for the Advancement of Science, August Hi. 
1894. 
