Ls 
818 LE. W. Hilgard on the Quaternary of Mississippi. 
nished by the rare, small, and well-worn pebbles of greenstone, 
porphyry, trappean rocks and even mica schist, which close ob- 
servation will detect among the shingle of the Mississippi-band; 
the direction of whose currents alone seem to forbid the deriva- 
tion of these rocks from any point as far south as the eruptive 
and primary region of Arkansas. It remains for future compart 
sons, however, to settle this point. 
As to the finer materials of this formation, it is significant that 
while the sharpness of the sand of the northern Drift deposits 1s 
often mentioned by writers on the subject, the sandgrains of the 
Orange Sand proper—that which forms the rocky hill-tops and 
the main body of the formation, are always very much rounded, 
as a proof of their transportation from along distance. Whe 
er or not the same is true of the Atlantic ridge of detritus men- 
tioned by Tuomey, I am not aware; but it does not seem to have 
struck that observer. ; 
Dr. D. D. Owen repeatedly mentions lignites and leaf-bearing 
clays of quaternary age, as underlying these deposits in Ken- 
tucky and Arkansas. Without calling in question the determin- 
ation of that eminent observer, I will state that I have found no 
reason to suspect any more special connection between the Or- 
ange Sand and any of the lignitic beds of Mississippi, than 1s af- 
forded by the obvious appropriation of the materials of the latter 
by the former formation—a relation existing equally where other 
formations underlie. , ney 
According to Mr, Lesquereux’s determination, the lignitic of 
North Mississippi is certainly not newer than the Miocene ; while 
some marine shells occurring in its highest strata, would seem to 
place it even below the lowest marine Kocene of the state 
($ 162, ff.). While so far as my observations reach, I find ye 
reason to suspect that all the lignitic strata occurring north 0 
the marine Tertiary in Mississippi and Alabama, are not of the 
same age, I have nothing to urge against the occurrence of qua 
ternary lignites elsewhere. Some of the lignitic beds of the 
Mississippi bluff (§ 181), of which I cannot speak from personal 
observation, may be of that age, as well as the small basin mel 
tioned (§ 27) as occurring in a section of Orange Sand in Ten- 
nessee. In the absence of pretty numerous determinations ° 
fossil plants, however, it must be difficult to decide upon the 
age of such strata, when not seen in juxtaposition with the ma- 
rine Tertiary. 
The Bluff, or Loess Group.—This stage of the quaternary ris 
uiriD 
‘Fr icksburg southward, it skirts the lett 
bank of the Mississippi river, with a width, inland, of twelve '° 
fifteen miles. It caps most of the high points visible from the 
