1912] | Bush,— Geographic Origin of Crataegus viridis 85 
Railway. Into this inland sea the ancient river was discharged ap- 
proximately one hundred miles south of Saint Louis, and the colony 
of southern arborescent species now found in that region is undoubt- 
edly a vestige of the semi-tropical forests that once bordered this 
ancient sea. Beyond this area, however, deposits of Tertiary age 
are but little developed in the Upper Mississippi Valley, and scarcely 
a trace of the fossilized flora has been preserved. 
It is a fact perhaps not without significance in this connection, that 
in southwestern Missouri and southeastern Kansas, where, as has 
been stated, a form of Crataegus viridis is abundant, many of the 
high hills are covered with a deposit of gravel, consisting of water- 
worn fragments of chert, undoubtedly of local origin, but indicating 
the former existence of a great drainage system towards the southwest. 
These deposits, which are particularly abundant about Webb City 
and Joplin, Missouri, have been designated by geologists as Lafayette 
Gravel and assigned to a time late in the Tertiary period. Over the 
higher elevations of the region they may be traced for many miles, 
indicating the course and magnitude of an ancient river, as in places 
they attain a thickness of from ten to eighteen feet. This region lies 
entirely beyond the area of glaciation, which embraced all of northern 
Missouri and extended a little south of the Missouri River, and this 
fact doubtless accounts for the preservation of the Lafayette deposits 
here, while certainly they would have been obliterated to the north- 
ward by the ice mantle and the floods that marked its recession and 
inundated the country far beyond its southern limits. 
The Mississippi River of that period, or its precursor, a small and 
unimportant stream discharging itself into the Tertiary sea, was 
doubtless bordered by forests of many species. It is reasonable to 
suppose that the viridis form of Crataegus would be borne down by 
the waters of this stream from its northern home and that individuals 
would establish themselves at intervals along its course and about the 
coasts of the ancient sea, following the ever extending limits of the 
land to the south, until at length a form appeared, the Crataegus 
viridis of Linnaeus, as we know it, which found a suitable habitat 
and attained a vast development in the low-lying coastal plains of 
the Gulf States. 
On the other hand, following the great drainage system to the 
southwest, other individuals of the parent species would establish 
themselves along its course and there enter into competition with 
