iene’ ps Sete rae 
a Se es! ah A ELE iets N 
GEOLOGICAL HISTORY OF THE GULF OF MEXICO. 519 
The currents must have been broad, powerful and deep, and operating ` 
be carried indefinitely. Agates and cornelians, whose home is in trap 
rocks above the Falls of St. Anthony, are found scattered along pen valley 
to the mouth of the Ohio. If they travel at the rate of only a 
year, three hundred and twenty years would find them saved a mile 
gulfward, and ten thousand years more than thirty miles. A current of 
four miles an hour, extending from the western base of the Cumberland 
Mountains in Tennessee to the foot of the Ozark Mountains in Missouri 
would fill tee a space equal to a large state in a century 
It appeared to the speaker that here is a simple and ‘sufficient explana- 
tion for hie translation, in the later parts of the ice period, of so much 
northern gravel non loam, and even of small boulders to the ieres of 
the gulf and into 
Below the states north of the Ohio, pieces of the native copper o 
Lake Superior are not found in the Quaternary gravel. The water forces 
netic iron boulders and gravel. Both the copper and the heavy iron ores 
of Lake Superior are common in the Drift of the Lake country, but they 
required the propelling force of moving ice to send them along. Beyond 
the ice or glacier field, deep and persistent currents of water were able to 
take up and move forward the lighter materials to places many hundred 
miles distant, provided the element of time is sufficiently great. 
1 this way we may synchronize the whole field of the Quaternary of 
the United States east of the Rocky Mountains and perhaps that of the 
Pacific slope. 
Dr. C. A. Warre was much interested in the able paper of Pro- 
fessor Hilgard, especially as hitherto so very little has been brought 
ena 
valley have not been mistaken in ours. In Iowa we have a very different 
set of Post-tertiary phenomena, and yet I believe true explanations of 
both may, and ultimately will be, completely harmonized by careful study 
of the broad region intervening between fhose that he and I have res- 
pectively studied. 
The Post-tertiary deposits of Iowa consist of the true, unaltered, un- 
stratified Drift, so well known in that region and elsewhere, through the 
more or less distinctly stratified gravelly or pargi drift observable in the 
oods, to 
valley sides above the rea fi alluvium of their flood- 
plains esides this, we,have, in West owa, that very kt ae 
deposit resting u e drift which Professor Swallow has called t 
B sit. This deposit, doubtless, ind essentially the same orig 
in 
as that to which Professor Hilgard has given ae same name in Louisiana, 
namely, in the muddy waters of the Missouri river, although the deposit, 
doubtless, never had direct continuity, but was interrupted by broad 
