The sediments of the Middle Devonian of the eastern United States form a great wedge with its thickest part in eastern New York and adjacent New Jersey. The wedge represents the filling of a great geosyncline; the feather edge of the wedge lies far to the west in Arkansas. Sedimentation was not continuous in the Midwest where di conformities occur. The lack of continuity of the sediments is a reflection of regional uplifts in all parts of the basin and margining lands; the minor breaks may be a reflection of climatic fluctuations.
The sediments composing this wedge consist of red and green nonmarine beds and conglomerates. To the west the sediments become wholly marine and are predominantly sandy in eastern and central New York, mostly shaly in western New York bul with fingers of limestone. In the shelf area of the shallow sea in the Midwest the sequence is predominantly limy except for local subsidiary geosynclines (auto-geosynclines) where the section, although mainly limy, thickens and contains considerable sand and shale.
Evidence furnished by the animals and plants shows that the lands on the east margin of the geosyncline were, in places at least, heavily forested, and the freshwater streams draining these areas were inhabited by fishes and pelecypods. The shore region of the east was populated by a fauna rich in mollusks, but as the sand content decreased so also did the percentage of mollusks. In the region of the fine shales brachiopods abounded, but in the shelf area of the Midwest with its probable shallow and well-lighted waters, corals and bryozoans were abundant. With them occurred plantations of crinoids and blastoids. Brachiopods were abundant in this region, but mollusks were scarce.
As in modern seas geographical localization of some species has been detected. It has also been noted that recurrence of faunal types took place in unexpected parts of the section. Even in those early days not all animals enjoyed a disease-free life because evidences of malady are recorded. Furthermore, the eternal struggle for food went on then as now, the strong and the quick devouring the weak and the slow, the meek and minute ultimately consuming the strong and the quick.