| Groups. | Formations. | European |
| | | Equivalent. |
+---------------+-------------------------------+-------------+
/ | Chautauquan. | Chemung beds with Catskill | Famennien. |
U | | | as a local facies. | |
P | | | | |
P < | ( | Portage beds (Naples, Ithaca | Frasnien. |
E | | ( | and Oneonta shales as local | |
R | | Senecan. < | facies). | |
. | | ( | Genesee shales. | |
\ | ( | Tully limestone. | |
+---------------+-------------------------------+-------------+
M / | Erian. ( | Hamilton shale. | Givetien. |
I | | ( | Marcellus shale. | |
D | | | | |
D < | ( | Onondaga (Corniferous) | Eifelien. |
L | | Ulsterian. ( | limestone. | |
E | | < | Schoharie grit. | |
. \ | ( | Esopus grit (Caudagalli grit).| |
+---------------+-------------------------------+-------------+
L / | Oriskanian. | Oriskany sandstone. | Coblentzien.|
O | | | | |
W | | ( | Kingston beds. | Gedinnien. |
E < |Helderbe- ( | Becraft limestone. | |
R | | rgian. < | New Scotland beds. | |
. | | ( | Coeymans limestone. | |
\ +---------------+-------------------------------+-------------+

Although the correlation of the strata has only advanced a short
distance, there is no doubt as to the presence of undifferentiated
Devonian rocks in many parts of the continent. In the Great Plains
this system appears to be absent, but it is represented in Colorado,
Utah, Nevada, Wyoming, Montana, California and Arizona; Devonian rocks
occur between the Sierras and the Rocky Mountains, in the Arbuckle
Mountains of Oklahoma and in Texas. In the western interior limestones