THE CAMBRO-SILURIAN QUESTION. 521 
Pacific, forty miles west of St. Louis and elsewhere, unmistakable 
evidences of a marked unconformity at this horizon. Now the 
Magnesian limestones and sandstones of the crystalline area, are, 
according to the best accounts, at a geological level considerably 
below the Saccharoidal sandstone. Regarding the age of the rocks 
Broadhead,’ who has been in the region more than any one else 
perhaps, is inclined to assign a large part of them to the Cambrian. 
Lately, Walcott? in his correlation essay on the Cambrian of 
North America, has summed up all that is known on the subject 
and has colored on his map of the continent as Cambrian all of 
the sedimentaries of the crystalline district of Missouri. 
The correlation of the Magnesian limestone of southern Mis- 
souri has been almost entirely upon very meager stratigraphical 
erounds,  Exom) one) end) of the broad) uplitt to) the vother; 
wherever the rocks of this series are open to view, there has 
been found up to the present time a great paucity of fossil forms. 
Not only are the rocks almost devoid of the ordinary faunal 
means by which the different terranes may be determined with 
precision, but the organic remains thus far secured are so poorly 
preserved that they are largely worthless for systematic purposes. 
Further, it is quite remarkable that of all the forms obtained 
from these rocks there have been none which have been identi- 
fied with certainty with species described from other districts. 
In every case where specific comparisons have been made more 
or less doubt has always been expressed concerning the actual 
identity of the species referred to. Ofthe many fossils mentioned 
in connection with the various allusions to, or descriptions of, 
the region, few of the references have been more than generic. 
In a recent critical review3 of the fossils of Missouri, collections 
made by different individuals from the Magnesian limestones 
were examined. The material proved to be so fragmentary on 
the whole, and the exact or even approximate horizons where 
the particular forms were obtained so poorly determined that 
t American Geologist, Vol. III, p. 7. Minneapolis, 1889. 
2U.S. Geol. Sur., Bulletin 81. Washington, 1891. 
3 Missouri Geol. Sur., Vols. 1V and V. Jefferson City, 1894. 
