5-i H. S. Williams — Different types of the 



tions, while the argillaceous and calcareous shales are more con- 

 spicuous in New York, Ohio, Canada West and Michigan. A 

 thousand feet may be taken as an average for the thickness, in- 

 cluding the two terminal black shales, though some of the Appa- 

 lachian sections double this thickness. In our accepted classifi- 

 cation the upper, Genesee black shale is grouped with the Ham- 

 ilton, but, as I have shown elsewhere, there are good reasons for 

 drawing the distinctive line, separating middle and upper De- 

 vonian, below rather than above the' Genesee shale. 



Above the Hamilton stage a period of deposition of arena- 

 ceous shales and sandstones prevailed all over this eastern area, 

 called the " Chemung Period " by Dana, and divided into the 

 Portage and Chemung stages. The deposits attain a thickness 

 of two or three thousand feet in New York and Northern 

 Pennsylvania, and farther south are represented by 5,000 feet 

 of sandy deposits, coarser toward the top, and with occasional 

 gravel conglomerates. This series of deposits is characteristic 

 of the eastern area, and is not recognized in the central or west- 

 ern areas. It is linked by its flora with the eastern border sec- 

 tions, and by its fauna is recognized as intimately associated 

 with the upper Devonian deposits of North Devonshire in 

 England. 



The faunas of the upper Devonian change rapidly in com- 

 position on passing westward from the Appalachian ridges, and 

 the pure Chemung tj^pe is scarcely recognized west of western 

 New York and Pennsylvania, although some of its species are 

 seen in the Iowa and Nevada sections. Passing into Ohio,. 

 Canada West and Michigan, the upper part of the Devonian 

 assumes a distinct type, which is more closely allied with that 

 of the Indiana and Illinois sections. It appears to be a prev- 

 alence of the conditions expressed in the Genesee shales and 

 associated Portage shales and sandstones of New York, with 

 the failure of the Chemung rocks and fauna, running up into 

 shales and sandstones of the Waverly and closing with con- 

 glomerates. The more eastern sections, after the Hamil- 

 ton, run up into sandstones, red and gray shales, sand- 

 stones of considerable thickness, and conglomerates, and 

 present no trace of any marine fauna intermediate between 

 the Chemung and the Carboniferous. As we approach the 

 Ohio border going westward the Chemung fauna also fails, 

 and the Waverly follows the Hamilton with only the fauna of 

 the black shales intervening. 



In the eastern part of New York, Pennsylvania and south- 

 ward, the coarse sands and conglomerates with red and green 

 shales, prevail after the Hamilton stage, reaching a thickness 

 of 6,000 or 7,000 feet, and then the Chemung fauna is sparse 

 and confined to the lower strata. This red shale and sandstone 



