IOWA ACADEMY OP SCIENCE 
149 
Eras 
Periods 
Snb-p. 
Series 
Terranes 
Thick. 
Rocks 
Marais des 
Cygnes 
800 
Shales. 
Des Moines 
Appanoose 
100 
Limestones. 
Oberokee 
250 
Shales. 
Carbonic 
Arkansan 
Interval 
Unconformity. 
St. Louis 
100 
Limestones. 
Spergen 
10 
Limestones. 
Warsaw 
65 
Limestones. 
Keokuk 
75 
Limestones. 
Mississippian — 
Burlington 
125 
Limestones. 
Chouteau 
50 
Limestones. 
Hannibal 
76 
Shales. 
Louisiana 
10 
Limestones. 
S avert on 
60 
Shales. 
Grassy 
50 
Shales. 
Oliattanoogan 
Interval 
Unconformity 
Late. 
Chemungan 
Lime Creek 
125 
Shales. 
Lucas 
25 
Limestones. 
Coralville 
30 
Limestones. 
Devonic - 
Seneean 
Rapid 
35 
Limestones. 
Solon 
25 
Limestones. 
O 
Unconformity. 
Q 
Payette 
75 
Limestones. 
s 
Mid 
Hamiltonian 
Independence — 
20 
Shales. 
c 
Otis 
10 
Limestones. 
Cloggan 
15 
Dolomites. 
Bertram 
35 
Dolomites. 
T.ntp 
Cower an 
Anamosa 
60 
Dolomites. 
LeClaire 
70 
Dolomites. 
Silurie 
Montecello 
• 60 
Dolomites. 
Mid 
Niagaran _ 
TT nrtwielr 
SO 
Dolomites. 
Colesburg 
30 
Dolomites. 
Sabula 
50 
Dolomites. 
Brainard 
125 
Shales. 
Atkinson 
40 
Limestones. 
T,nt^ 
Maquoketan 
Clermont . . 
15 
Shales. 
Elgin 
75 
Shales. 
Ordovicic 
Galena 
225 
Dolomites. 
Mid 
Mnhawkinn 
Deeorah 
30 
Shales. 
Plattville 
100 
Limestones. 
Glenwood 
15 
Shales. 
Early 
Minnesotan — — 
St. Peter 
100 
Sandstones. 
Shakopee __ 
75 
Dolomites. 
T.ntp 
Ozarkian 
New Richmond 
25 
Sandstones. 
Oneota 
160 
Dolomites. 
r!nmhrif» 
Jordan 
100 
Sandstones. 
Mid 
Croixnn 
St. Lawrence - 
50 
Dolomites . 
Dresbach 
150 
Sandstones. 
Early 
Interval 
Unconformity. 
Azoic 
Hnronie 
Latfi 
Siouan 
• 200 
Quartzites. 
For their usage here three groups of names need perhaps some little explana- 
tion. The terms applied to the terranes of the Niagaran series, the Senecan 
series and the Cretacic period have never been specifically defined. Soon after 
the organization of the Geological Survey of the State, when I had charge of 
