L. W. Hilgard—Geology of the Southwest. 267 
As regards the later formations, I note that the propriety of 
substituting Dana’s prior name of ‘Champlain period” by tha 
of “Bluff period,” as proposed and carried out by Prof, Hopkins, 
Stems to me at least doubtful. A descriptive name should at 
least give the predominant and essential character of the greater 
part of the formations concerned. That Swallow’s name, as 
applied to the Loess, is preéminently characteristic, no one that 
nows that formation, as invariably exhibited on the Mississippi 
and its great tributaries, will deny; while, apart from the Port 
Hudson bluff itself, few, probably, besides Prof. Hopkins and 
myself, know of any prominent example of bluffs formed by the 
ort Hudson strata—a formation as positively characterized by 
Plateaus and prairies, from Pensacola to the Rio Grande, as the 
oess is by “bluffs.” As for the Yellow Loam and its equiv- 
alents, spread like a blanket over the whole country, up hill 
pe carn, it is peculiarly apt, ¢f tn stu, to be absent from b/uf? 
S 
The name apart, I am constrained to believe that, while appar- 
ently differing widely from me in his interpretation of the strata 
penetrated in the New Orleans artesian well of 1856, he never- 
theless agrees, substantially, in all but the use of a name. 
when, on p. 185, he speaks of the Port Hudson strata as “the 
delta formed by the Mississippi, from the end of the Drift 
eriod to the beginning of the era of the Loess,” he merely 
ers from me in conferring the name of the ‘ Mississippi’ 
"pon that broad expanse of swamps, marshes, and lagoons 
Which then filled the trough remaining after the Drift period, 
and through which the continental waters made their way as 
t they might. In this broad sense, I cheerfully admit the 
Whole of the strata underlying New Orleans to be “ Mississipp! 
delta, deposits.” Similar ones, however, were at that time 
forming all along the northern and western Gulf border, con- 
Stituting the “blue clay bottom ;” which, is as well known on 
the coast of Alabama and Texas, as is the sudden seaward 
Slope at a variable distance from the main land, that Prof. 
Hopkins erroneously supposes to be peculiar to the mouths of 
the Mississippi, and to be formed by river deposit. 
_But while the modern delta deposits proper everywhere ex- 
hibit an abundance of drift-wood particles, and a rapid alterna- 
tion of character corresponding to the frequent rise and fall of 
the river: the deeper deposits of the New Orleans well lack both 
these characteristics, bemg remarkably uniform through consid- 
erable thicknesses of material.* — the — * far as pre- 
viously known are of livi cies; but so far as [ am aware, 
nothing else is expected of asiueenry marine beds. Yet the 
fact that three or four of the species are not now known to be 
* See “ Report on the Age of the Delta,” in Rep. U. S. Eng. Dept. for 1870. 
