DEVONIAN. 313 



gray sandstones. These rocks are nearly unfossiliferous, containing only an occasional specimen 

 of Archseopteris and Amnigenia catshillensis (Van.) Hall. The formation has a thickness of 

 550 feet in the Chenango Valley and as the physical conditions under which the Oneontawas 

 deposited appeared earlier to the eastward, it gradually thickens in that direction till in Albany 

 and Greene counties it completely replaces the Ithaca formation. 



The Chemung formation east of the Susquehanna River rapidly thins to the eastward on 

 account of the earUer appearance of the physical conditions which prevailed during the deposi- 

 tion of the Catskill formation, so that the Hthologic characters of the Chemung are gradually 

 replaced by those of the Catskill, and as this change takes place the Chemung fauna disappears 

 till the farthest east it was noted was near Spring Lake, northwest of Delhi, where a small 

 Chemung faunule occurs above red shales. Search in the rocks occurring at the horizon of the 

 Chemung formation east of the Delaware River was not rewarded with any fossils, and the 

 lithologic appearance of these rocks is similar to that of those composing the Oneonta and 

 Catskill formations. 



In eastern New York in Albany, Greene, Ulster, and Sulhvan counties the physical 

 conditions under which the Oneonta and Catsldll formations were deposited began as early 

 as Sherburne time and continued throughout the remainder of the Devonian period. The 

 representation of the Ithaca or Chemung faunas is very slight and this great mass of rocks 

 consists mainly of alternations of red and green shales and sandstones and gray to greenish- 

 gray coarse-grained sandstones, with some conglomerates in the Catskill Mountains. In the 

 Delaware Valley the red rocks do not appear as early and there is some representation of the 

 Ithaca fauna, which is more pronounced in northeastern Pennsylvania. As this series of rocks 

 is followed along the Appalachians southwesterly across Pennsylvania, Maryland, and the 

 Virginias it is found that the reds gradually appear later and the Chemung fauna is present. 

 For in western Maryland, succeeding the black shales with a Genesee fauna at the top of 

 the Hamilton, are first nearly barren smooth shales and sandstones like the Portage of western 

 New York, then rougher shales and rather mealy sandstones containing an abundant Chemung 

 fauna with numerous specimens of Spirifer disjunctus in Garrett County, and finally the red and 

 grayish shales and sandstones of the Catskill. This change from the Catskill Mountain region to 

 the southwest is found to be quite similar in general characters to the change from these moun- 

 tains westward across southern New York, the story of which was excellently told some years 

 ago by Prof. Stevenson in his address before the American Association for the Advancement 

 of Science." 



K-L 16-17. MICHIGAN, INDIANA, AND OHIO. 



The Michigan section of the Devonian comprises the Dundee Umestone, Trav- 

 erse formation, and Antrim shale. 



Lane ^" describes the divisions of the Devonian, and from his description the 

 following notes have been derived. 



The Dundee limestone is a persistent stratum throughout Michigan, with a 

 general thickness of 200 to 253 feet. "Beginning with a thickness of an even 100 

 feet in the southeast corner of the State, it thickens slowly to Port Huron. Going 

 west and north it at first thickens until it gets its full thickness of about 250 feet, 

 and then begins to thin." It is nearly the equivalent of the Onondaga ("Cornif- 

 erous") limestone of New York. "It is very uniformly a high-grade limestone, 

 with only a small percentage of magnesia, not infrequently over 98 per cent CaCOs, 

 light colored, or brown with oily matter * * * ^^d sometimes, not always, 

 cherty." 



« The Chemung and Catskill (upper Devonian) on the eastern side of the Appalachian basin: Proc. Am. Assoc. 

 Adv. Sci., vol. 40, 1892, pp. 219-248. 



