340 The American Geologist. May, 1897 
erosion which Hersh?y has named the Ozartcian epoch, seem 
to me better referred, as constituting together tlie Lafayette 
period, to the Quaternary than to the closing part of tiie Ter- 
tiary era, in which they are placed by McGee and others. 
Hershey takes the middle ground of referring the epoch of 
Lafayette deposition to. the end of Tertiary time, and the 
Ozarkian elevation and erosion to the beginning of the Qua- 
ternary era.* To my mind, however, it seems quite certain that 
the continental disturbance expressed in the Ozarkian epeiro- 
genic uplift was earlier manifested in the deposition of the 
Lafayette beds. Indeed, these beds appear to me to belong to 
the initial stage of continental elevation, as deposits of flood- 
ed rivers overloaded by the erosion of residuary clays and 
valley gravel and sand along the upper parts of the stream 
courses, due to the incipient epeirogenic uplift, but laid down 
on the coastal plains above the sea level, where the decreased 
gradients and slower currents of the streams no longer permit- 
ted them to carry forward their load. But when the uplift 
became greater, in the Ozarkian epoch, all the marginal plains 
shared wnth the uplands and mountain regions in deep and 
widely extended erosion. 
Ozarkian Elf:vation, in its Culmination, the Cause of 
THE Ice Age. 
To some glacialists, it has seemed to be a ditKculty, if great 
altitude was the cause of the cold and snowy climate produc- 
ing the ice-sheet, that the fjords and submerged continua- 
tions of river valleys eroded when the northern lands stood 
much higher than now, but yet had no ice covering. It may 
be readily answered, however, that the long continuation of 
the upward movement, before reaching its culmination, al- 
lowed the streams to erode the fjords to depths 1,000 to 3,000 
feet, or more, below the present sea level, while the bottoms 
of the fjords were so raised as to be land valleys; and that 
later the elevation reached its maximum and was contin- 
ued so long that the slow accumulation of snow from year to 
year formed ice-sheets hundreds and even thousands of feet 
thick, enveloping the north half of North America and north - 
*Ara. Naturalist, vol. xxxi, pp. 104-114, Feb. 1897. Compare the Am. 
Geologist, vol. xvii, p. 389, June, 1896. 
