The Hfiobrara Chalk. — Calvin. 151 
In 1870 Dr. Charles A. White, in discussing the Inoceramus 
beds along the Sioux river, which are in Iowa the equivalent 
of the Niobrara of Meek and Hay den, tells us that, among 
other fossils, ''minute Foraminifera (probably Globulina) are 
sometimes met with in great numbers."* 
The article by Dr. G. M. Dawson, already cited as appear- 
ing in the Canadian Katuraliat for 1874. marks a very impor- 
tant step in advance of all previous publications in the matter 
of investigating the origin and composition of the Niobrara 
chalk. The strata of Manitoba that were the subject of in- 
vestigation are the northward continuation of the chalk beds 
of our Sioux river region, and Dr. Dawson was able to com- 
pare microscopically the Manitoban with Nebraskan material. 
The article is illustrated with figures of Foraminifera. and 
speaking of this group of organisms he says: "The general 
facies of the foraminiferal fauna of the Cretaceous rucks of 
Manitoba and Nebraska singularly resembles that of the ordi- 
nary English chalk. Both abound in Textularine and Rotaline 
forms of similar types.'" 
Dr. Dawson's paper, however, owes its chief importance to 
the fact that it is the first, so far as J know, that recognizes 
coccoliths as agents in the formation of American chalk. Coc- 
coliths, in my judgment, are much more characteristic of chalk 
than Foraminifera. Individually they are thousands of times 
more numerous, and collectively they make up a much Larger 
proportion of the bulk of true chalk than do the larger and 
more obtrusive foraminiferal shells. Chalk composed of Fo- 
raminifera. either broken or entire, is harsh and rough and 
unsuited to many purposes to which this substance is applied. 
( occoliths on the other hand rarely exceed the one-hundredth 
of a millimeter in diameter, and chalk formed out of such 
minute bodies is soft, works smoothly on blackboard or chalk 
line, and may be ground between the fingers to an impalpable 
powder. Dawson's paper is illustrated with a number of 
figures showing the characteristic appearance of coccoliths 
under a high amplification, and along with the coccoliths 
there are illustrations of a number of the minute calcareous 
rod-like objects to which the name rhabdolithe has been ap 
plied. Relatively speaking, rhabdoliths are not common in 
•Geology of Iowa, Dr. C. A. White, Vol. i. p. 294, 1870. 
