The Senecan series is composed of shallow-water deposits; the Tully limestone, a local bed in New York, thins out in places into a layer of pyrites which contains a remarkable dwarfed fauna. The bituminous Genesee shales are thickest in Pennsylvania (300 ft.); 25 ft. on Lake Erie. The shales and sandstones of the Portage formation reach 1000 ft. to 1400 ft. in western New York. In the Chautauquan series the Chemung formation is not always clearly separable from the Portage beds, it is a sandstone and conglomerate formation which reaches its maximum thickness (8000 ft.) in Pennsylvania, but thins rapidly towards the west. In the Catskill region the Upper Devonian has an Old Red facies--red shales and sandstones with a freshwater and brackish fauna.
+---------------+-------------------------------+-------------+ | | | Probable | | 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. | Givétien. | I | | ( | Marcellus shale. | | D | | | | | D < | ( | Onondaga (Corniferous) | Eifélien. | L | | Ulsterian. ( | limestone. | | E | | < | Schoharie grit. | | . \ | ( | Esopus grit (Caudagalli grit).| | +---------------+-------------------------------+-------------+ L / | Oriskanian. | Oriskany sandstone. | Coblentzien.| O | | | | | W | | ( | Kingston beds. | Gédinnien. | 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 predominate; 6000 ft. of limestone are found at Eureka, Nevada, beneath 2000 ft. of shale. On the Pacific coast metamorphism of the rocks is common, and lava-flows and tuffs occur in them.