Geology and Mineralogy. 418 
also often found, especially in Lancaster county. In Lincoln, 
situated “near the western shore of the Missouri lake of the 
period,” “ dey have been found in at least twenty wells. Pro- 
face, underneath the second bed of black soil. “It appears then 
that some old races lived around the shores of this lake, paddled 
thei canoes over its waters, and accidentally dropped their arrows 
in its waters or let them fly at a passing water fowl.’ e rising 
of the land “closing the less period first clearly outlined the 
present rivers of Nebraska.” 
At the present time the rivers have very wide river-bottoms, 
ranging from one to ten miles or more. Above these there are 
one or more terraces: a — usually 3 to 6 feet abers the river- 
2 to 5 feet ; and a third, of varying eleva- 
tion. The bottom-lands are ie i overflowed in any part at the 
highest floods. 
2. Silurian age of the Crystalline rocks of Eastern Pennsyl- 
vania and Hudson River age se the A Ady tc Schists.—Mr. 
om a 
6 
[wal 
a 
5 
5 
TM 
$} 
TR 
2 oO 
co) 
5 
= 
Ru 
Charles E. Hall has an important paper on this subject in the 
Proceedings of the American Philosophical Fare oe es January, 
1880, together with a map illustrating it. He first mentions the 
second, from the vicinity of the last shes ae cawand 
across ‘thie ‘Schuylkill, and covering much of northern Delaware 
unty. 
(2) Pot sdam sandstone and conglomerate, with some schistose 
beds resting unconformably on the preceding ; over these, dolo- 
hydromica schists, the upper part of which group has — 
Trenton fossils at Sonkegeo Bucks County; and a 
beds of quartzite and serpentine, sere the Hudson River 
Sroup, and flank the Chester Valley on outle. saint from some point 
not far east of the Schuylkill River throughout the entire length 
of the valley; and micaceous garnetiferous schists with limestone, 
in the sd A central portion of pe County, resting Fea 
the last-mentioned hydromica schis These Hudson River 
schists are those that have been elisa Poeakie Details are given 
