144 The American Naturalist. [February, 
i General Notes. 
GEOLOGY AND PALEONTOLOGY. 
Paleozoic Formations of Southern Minnesota.—A sys 
tematic account of the Paleozoic formations of southeastern Minnesota, 
by C. W. Hall and F. W. Sardeson, is given in the Bulletin of the 
Geological Society of America for 1892. The rocks described occupy 
an area some 13,200 square miles in extent. They stretch eastward 
from a straight line between Mankato and Hinckley to the State of 
Wisconsin, and from Chengwatona southward to Iowa. These periods 
of geologic time are represented by three formations: Upper Cam- 
brian, Ordovician, and Devonian. These Paleozoic rocks are under- 
lain by the Archean and Algonkian, and lie beneath patches of Cre- 
taceous and a covering of quaternary débris save in the extreme south- 
eastern corner included in Chamberlin’s “ driftless area.” 
The Upper Cambrian is represented in this region by the Potsdam 
sandstone and the Magnesian series ; the Ordovician by the St. Peter, — 
the Trenton, and the Cincinnati beds. The Devonian is present in so 
thin a layer in which so few fossils occur that it cannot be assigned to 
any division of that group, but is supposed to belong near the middle. 
The writers give the following summary of thickness and leading 
lithological characters based chiefly upon their own measurements and 
determinations : : 
FEET. 
Devonian. Not subdivided. php be and shale 10-15 
( Cincin- f Wyko Limeston 20 70 
nati. | Maquoketa. Shale at limestone 20 
Maclurea “sins re 
j Lingulasina limes 
= Camar nas shaly risen » 
: | Orthisina calcareous shale 
Ordovician } Trenton 4 Zyeorpire shale Be 
0 
Stictopora shal 30 
L Speco can ey bees Tamer añd shale 10 
Blue rosi .12 = 
Bu Paroa 15) “u 
_ Saint Peter, not subdivided, iiio 15-11 an 
t Shakopie dolomite 10-5 | 
evator B (Ric hmond) medics 
Magnesian, piin Sapa dolomite 
Jordan sand 
Caelio. 1 Saint Law kka me Malisacties and shales 
Raden not subdivided, sandstones and shales 
Total thickness of Paleozoic strata in Minnesota........++++ 
< 
ined 
S 
