Tee Cm nga SMe Paty Saas A Aiea oe 
80 ae 
GEOLOGICAL HISTORY OF THE GULF OF MEXICO. 523 
to the elevations which brought up the Apallachians and the Rocky Moun- 
h 
of Lake Superior, the northern and southern Drift are continuous, becom- 
ing smaller as you go south, borne there by the oceanic currents, and 
afterward, as the land rose, dropped in the form of fresh water deposits, 
accounting for the large boulders in the north, the beds of gravel in the 
south, the beds of peat and all the varied et gai that have been ob- 
served in connection with the subject of the Dr 
Professor HimGarp remarked, in reply, that, in Pe South at least, 
achi 
ing positio n i 
southern stratified Drift corresponded to the ‘ modified Drift” of the 
West, though on a very large scale; but it would not do to call it by that 
name, which could apply only to a small rtion in the axis of the em- 
baydient: Elsewhere it was modified CUNG ola Cretaceous and Ter- 
tiary; the materials of these formations having been s aA plowed up 
and redeposited farther south by the Drift waters. No na e could be 
altogether distinctive and characteristic, yet in this case the PARER 
a very great degree, and he thought the name of * Stratified. 
Drift” might properly be made to embrace the southern Drift as we ell as 
the ‘‘ modified” Drift of the Western States. 
t the present time, the winter ice of the ge i frequently runs 
past Vicksburg. How much more must the ice-floes and bergs of the 
Glacial period have reached at least shat latitude, ae to which we find, 
even though rarely, boulders of northern derivation, too ponderous and 
too little worn to have been transported by water alone. Quartzite peb- 
bles of a couple of pounds weight occur even at the island of Petite Anse, 
together with other smaller ones of northern rocks; and a profusion of 
those derived from the Grand Gulf rocks, whose nearest outcrop lies 
about sixty miles due north. 
In ly to a question as to what he now thought of the age of the rock- 
salt sépa of Petite Anse, Prof. HıLearD stated that he thought it of the 
ta 
nd 
militated against its connection with any of the Tertiary stages. On the 
other hand, the Cretaceous of northern Louisiana was es salt- 
