384 The American Geologist. June, 1902. 
DETERMINATION OF THE CAMBRIAN AGE THE 
MAGNESIAN LIMESTONES OF MISSOURI. 
By CHARLES R. KEYES, Des Moines, Iowa. 
In many places in the recent reports of the Missouri Ge- 
ologicel Survey, certain formations comprising the lower part 
of the great Magnesian limestone sequence—the Ozark series 
of Broadhead—of southeastern Missouri, are referred to as 
Cambrian in age. Many of these references to the Cambrian 
are without special qualification, or adduced proofs of state- 
ment, just as is frequently mentioned the geological age 
of any terrane, the relationships of which to associated for- 
mations are thought to be well understood. Some of the ref- 
erences to the Missouri Cambrian are, however, more than 
merely incidental in import. It is the purpose of the present 
note to call attention to the character of some of the data upon 
which was based the assignment of a Cambrian age to a con- 
siderable part of the section which had long been called Sil- 
urian; and to point out that the proofs are even very much 
more conclusive than is indicated by any that have been men- 
tioned in print. 
Lately, several articles have appeared in which the real 
significance of the published data of the Missouri Survey 
seems to be overlooked. In one of the most recent of these 
papers™, some of the references in the Missouri reports are 
pointed out as evidence that the foundation for the determin- 
ation of the Cambrian age of the southeast Missouri terranes 
was insufficient; and additional notes are offered as the first 
definite facts to be adduced on this subject. 
Ever since the publication of the Paleontology of Missouri, + 
the geologists of that state have been conscious of the de- 
sirabilitv of havine published at the earliest opportunity all 
the evidence bearmg upon the Cambrian age of most of the 
great Magnesian limestone series of the Ozarks. At the time 
that the general paleontological reports were issued considera- 
ble data relating to this phase of the subject had been already 
accumulated, but as the original manuscript which had been 
completed two years before, had been greaty expanded just 
* Am. Jour. Sci., (4), vol. xii, p. 302, 1901. 
+ Missouri Geol. Sur., vols. iv and v, 1894. 
