THE DEVONIAN PERIOD. 423 



fauna have here an extensive development. In northern Maine (Moose- 

 head Lake region) the Lower Devonian series (probably with other 

 undifferentiated beds) is reported to have a thickness of several thou- 

 sand feet. 1 From the testimony of fossils, both European and Ameri- 

 can, it is supposed that there was shallow-water connection between 

 eastern North America and southern Europe, allowing marine life not 

 at home in deep water to pass from the one continental region to the 

 other. 



The Middle Devonian. 



Local eastern formations. — In the east the Oriskany formation 

 is succeeded by other clastic beds (Esopus, formerly called Cauda 

 Galli, and Schoharie grits). Their equivalents have not been differ- 

 entiated west of the Appalachian region. These formations are rela- 

 tively thin, and are made up of sediments accumulated near shore. 



The Onondaga. — They are succeeded by the Onondaga limestone r 

 which is much more widely distributed, spreading from New York 

 on the east to the Mississippi. Within this area, the Onondaga rests, 

 now on Silurian 2 (Niagaran or later) beds, and now on Waterlime, 3 

 often with little evidence of unconformity, and with no intervening 

 beds which carry an Oriskany fauna. 



During the Onondagan epoch, the connection between the Atlantic 

 and the interior by way of the Chesapeake region appears to have been 

 closed (Fig. 193) but the descendants of the Oriskany fauna which 

 had entered the Mississippi basin while the passage was open, arc to bj 

 recognized in the fauna of the Onondaga limestone. 



The lower beds of the Onondaga limestone may have been in process 

 of deposition over the eastern interior while the Esopus beds were 

 accumulating in the Appalachian belt. If this be the case the con- 

 ditions for limestone accumulation were presently extended eastward 



1 Williams and Gregory, Bull. 165, U. S. Geol. Surv., p. 22. 



2 Geol. Surv. of Iowa, Norton, Vol. IV, p. 127, and Calvin, Vol. VII, p. 54. See 

 also Simonds, Arkansas Geol. Surv., Vol. IV, 1888; Hopkins, Vol. IV, 1890; Vol. II, 

 1891; Williams (H. S.), Vol. V, 1892. The presence of Middle Devonian strata in 

 Arkansas is uncertain. 



3 Blatchley and Ashley, 22d Ann. Rept. Dept. of Geol., etc., of Indiana; and 

 Sherzer, Geol. Surv. of Michigan, Vol. VII, p. 37; so also in Missouri, see Missouri 

 Geol. Surv., Vol. XII, p. 67, and 22d Ann. Rept. U. S. Geol. Surv., Pt. II, p. 85;. 

 and Shepard, Missouri Geol. Surv., Vol. XII, pp. 67-82. 



