THE DEVONIAN PERIOD. 439 



an outlier in the usual sense of that term. The remnant, quanti- 

 tatively insignificant, occurs in a fissure in the Niagara limestone, as 

 illustrated by Fig. 201. The limestone was apparently fissured before 

 the Devonian above was deposited. Portions of the Devonian sedi- 

 ments fell into an open fissure, carrying with them distinctive fossils 

 (fish teeth). In this protected position, the Devonian fossils escaped 

 removal. 



About much of the pre-Devonian area of southern Missouri, the 

 Carboniferous and Silurian beds stand in the same surface relations 

 as in northern Illinois, though Devonian probably appears between 

 these systems in the southwestern part of the State. It is thought by 

 some that most of the Ozark area was land during the Devonian period, 

 and that the Carboniferous sea lapped up on it farther than the 

 Devonian sea had done. The alternative view has been mentioned 

 (p. 433). Similar relations are repeated in the Black Hills, in Texas, 

 and at other points in the west, where the Devonian system outcrops 

 more rarely than any other system of the Paleozoic except the Silurian. 



As in the case of other systems, it is to be remembered that the 

 line on the surface marking the junction of the Devonian with older 

 formations in any particular region is not the line which marks the 

 limit of the Devonian sea in that region. Erosion has shifted the 

 outcrop of the system, and therefore the line of its junction with older 

 formations. Erosion, too, has reduced the aggregate area of the 

 Devonian as originally deposited. 



Igneous rocks. — The general absence of igneous rocks in most parts 

 of the well-known Devonian of the continent is to be noted; but in many 

 parts of the west, and also in central New York, 1 the Devonian strata 

 have been affected by dikes and intrusions of later times, and in Nova 

 Scotia and New Brunswick there are igneous rocks which appear to be 

 of Devonian age. 2 



Close of the Devonian. 



The general period of quiet which had prevailed during the Devo- 

 nian seems not to have come to an end at its close. Only in the eastern 

 part of the continent, in Maine, Nova Scotia, New Brunswick, and 



1 Matson, Jour, of Geol., Vol. XIII., p. 264. 

 'Williams, Jour, of Geol., Vol. II, pp. 17-19. 



