THE MISSOURI AND PLATTE RIVERS, ETC. 65 
species, but there has not been sufficient time to make the aes 
comparisons. Dr. oa Girard, to whom I have exhibited them 
coincides with me the opinion that they are new, and we propose 
for them aiovoGATy the names Helix socialis, and Planerbis antiqua. 
5. Stratum from bottom. 
Land 10 to 15 feet thick; not represented in the collection. 
f. 6. Stratum from bottom. 
_ This specimen is a compact white or grayish-white ee ia 
stone. The silicious grains are very uniform in size; quite small and 
po Stag to some lang from the Llavio ie pot brouayt in oy 
t 
weather. You inforra i me that this is the case, see that its thickness 
is about five feet, 
Aes ee layer, of apne. 
e from your description that ‘dees BPS layer of sand, which 
caries. fain 50 to 100 feet in thickness, is an ai ccumulation of drift 
sand or dunes, which was not — down under sat in the position 
which it now occupies. The rounded sloping surface which it presents 
towards the edge of the bluff, te its loose condition, and is additional 
ee 5 o drifted character. Undera glass, the sa ape apatites the 
sand hills on the Llano Esta 
The specimens from this eine oF the. bluff are ee by. two 
; the ridge 1 ee the vicin- 
= 
i 
pork 
a 
ae 
Places a ars in “se ers or seams, as if it had been. ; 
an es naan seme the eal” ‘ to ‘analy 
