‘ 
E.. Desor on the Post-Pliocene of the Southern States. 57° 
and are therefore referable to a Jater period in which the climate 
may actually have been colder. This however is a mere hy- 
The foregoing remarks apply more especially to the boulders 
along the sea-shore from New England to Long Island and part 
of New Jersey. From all the evidence we possess it seems 
highly probable that they were transported on ice-rafts along the 
sea-shore and stranded on the ridges and eminences which were 
then shoals along the coast. The next question then is, whether 
this mode of transportation applies likewise to the boulders occur- 
ring in the interior of New York and Pennsylvania, or whether 
we have to look for another agency:2 
It has been stated before that the last boulders of northern 
origin occur in New Jersey, alittle south of New York. But 
according to Prof. H. D. Rogers, they are chiefly limited to the 
sea-shore, and it would appear as if the highlands of New Jersey 
had acted as a barrier, preventing them from. spreading south, 
except through the channels of the rivers. Indeed there can be 
no doubt that the few boulders in the neighborhood of Philadel- 
phia are confined to the valleys, and on ascending the uplands in 
the neighborhood of the city we find that they disappear. The 
valley of the Delaware was such a channel by which a few 
northern boulders were conveyed farther than they would other- 
wise have reached. 
The valleys of the Susquehanna and the Potomac contain 
also a great many boulders, but those of the latter, it seems, are 
without exception derived from the Appalachian chain itself, 
Whereas among those of the Susquehanna, there may be some 
mountain. According to Prof. H. D. Rogers, there are evidences 
in each of these valleys of a violent-rusli of waters, which is 
Supposed to have carried along with it the boulders. which the 
valleys contain. But whether the same can be said of the boul- 
* Tt might rhaps be assumed on hygrometric principles, that the area of water 
being greater it the anaes ae elec eiasien of the boulders, there was a greater 
amount of evaporation causing more moisture and consequently mo and ice. 
Stconp Szams, Vol. XIV, No. 40.—July, 1852. 8 
a 
