354 New York State Museum 



ilarly placed Old Red Sandstone farther north belonged 

 to a new system. To these rocks in 1837 the name 

 Devonian was given from the exposures in Devonshire 

 which then became the type section, though a far bet- 

 ter section of Devonian rocks is found in western Ger- 

 many and adjoining areas in Belgium. As with the pre- 

 ceding systems, North America again furnishes the most 

 complete record. The rocks here are preserved over wide 

 areas and, unlike the type section, are for the most part 

 little disturbed. New York State again furnished the type 

 section for the American Devonian and hence, in a way 

 for the world. Other important exposures occur in Appa- 

 lachian areas and in Michigan, the latter extending into 

 Wisconsin and Iowa and also into Ohio, Indiana and 

 Ontario. In certain areas as in parts of the western half 

 of the Middle Appalachian region the transition from the 

 Silurian to the Devonian is so gradual that the boundary 

 between the two systems has been long in doubt. Until 

 recently the Helderbergian formations were placed in the 

 Silurian and the Oriskanian at one time was even in- 

 cluded in the same system. Helderbergian limestones, 

 with some interruptions, occur from southwestern Vir- 

 ginia to Albany, N. Y. along the Appalachian line. 



Geology. At the close of the Silurian or the begin- 

 ning of the Devonian there was an almost complete emer- 

 gence of the continent of North America, and at no time 

 during the Lower Devonian epoch was more than ten 

 per cent, of the continent submerged. The continent of 

 Appalachia at this time was extensive and probably a 

 broad mountainous upland with its eastern boundary ex- 

 tended perhaps 50 miles or more beyond the present con- 

 tinental shelf. The character of the sediments indicates 



