1891.] 
267 
| Shaler. 
that any such period as ten thousand years is insufficient to ac- 
count for the northward spread of these slow -marching forms. 
We cannot well conceive that if all our hickories and walnuts 
were removed from the northern forests down to the southern 
line occupied by the glacial ice, that they would succeed by the 
operation of all the agents of dissemination which we have noted 
in moving to the northward as far as they have attained at any- 
thing like the average rate of a mile in a century. If these forms 
occurred only sporadically in the northernmost part of the field 
which they occupy we might suppose that their implantation was 
due to chance action : The fact however that they extend in a 
continuous line from the Atlantic to Minnesota indicates that the 
advance has been accomplished by causes of a general and continu- 
ous nature. 
It thus seems to me that from the distribution of these large 
seeded trees we are led to the conclusion that any such period 
as ten or even twenty thousand years is totally inadequate to 
account for the changes which have taken place in the distri- 
bution of our forests since the close of the glacial period. 
The subject being thrown open to discussion, Mr. Upham sug- 
gested that the advance of the heavy-seeded trees northward 
might have been somewhat dependent on human agency, sup- 
posed paleolitlis having been frequently found in glacial detritus. 
He stated on the authority of Prof. Geikie that in Europe, where 
the Paleolithic and Neolithic stages of civilization can be readily 
distinguished, man had reached the more advanced condition 
before the close of the Glacial Period, and added that from con- 
siderations of the rate of advance of civilization as suggested by 
archaeological research, it seemed probable to him that subse- 
quent civilization from that point up to the present stage could 
have easily been accomplished in 7000 to 10,000 years — the time 
which, from the study of lakes and waterfalls, many geologists 
suppose to have elapsed since the retreat of the last continental 
ice-sheet. 
Prof. W. M. Davis read a paper entitled “ Illustration of the 
faulted monoclinal structure and topographic development of 
the Triassic formation of Connecticut by a working model.” 
