The Galena and Jlaqnoketa Series. — Sardeson. 189 
one distinguishing featvire. In the Bellerophon bed (li) R. 
minnesotensis is more typical; in the Stictoporella bed (3) Jt. 
minnesotensis and K. ainsliei are associated with Plertanihonites 
sericea, sensu siricto: in the Stictopora bed (4) Ji. minneso- 
tensis is found; in the Fucoid bed (5) li. increbescens, P. seri- 
cea, and 0. rogafa ; in the Orfhisina bed (O) E. increbesceus 
and var. laticostata, P. minnesotensis and O. royata; in the 
Caraarella bed (7) the same are rare and var, laticostata is 
not known; in the Lingulelasma bed (8) are R. capax,, rare, 
P. gibbosa, P. cf sericea, rare, and O. rogafa ; in the Macliirca 
bed (9) none of these three groups of fossils are yet known: 
in the Triplecia bed (10) R. capax,vnve, P. pva^cosis, 0. corpu- 
lenta, O. porrectn and O.futilis are found: in the Diplograp- 
\Vi9,\)i'(\ {11) 0. jjorrect a is locally a secondary'- fossil ; in the 
Orthoceras bed (12) P. sa.cea, O. emacerafa, and locally 0. 
multisecta •. in the Leptsena bed (13) li capax,P. recedens, O. 
corpalenUi, O. emacerata, O. futilis, and 0. ignota : in the 
Orthis bed {11) R. capax, li. anficosfiensis, locallj' P. neena/t, 
and R. perlamellosa, P. recedens, O. emacerata and O. tersa. 
Having determined the horizons or beds in the manner 
stated, and knowing the tlisti-ibution of our fossils, we are en- 
abled to compare them and it is at once conspicuous that the 
hypothetical times or intervals in which evolutionai-y changes 
took place do not coincide in different groups of species. For 
example, Rhynchonella m in nesotensis (1 to -1) changes abruptly 
to R. increbescens, (5 to 7) between beds four and five; Plec- 
tarnbonites serieea (3 to 5). changes likewise to P. minnesoten- 
sis (6,7) between beds five and six; Orthis rogata ranges 
from No. 4 to 8, not changing between four and five, nor five 
and six. 
The source of the different "varieties"' is either sudden and 
obscure evolution, or is from immigration of already different, 
contemporaneous species, and since the same ''varieties" are 
found in other areas it is certain that immigration is at least 
the scource in most cases. It is evident that species were ar- 
riving and departing from the area during the building of 
the two series so that there is found a steady change of fau- 
nal peculiarities. Most often they (uime or departed during 
the interval between the beds, the same being thus divisional 
lines in the series. Some species may have evolved and others 
