74 AMADEUS W. GRABAU 



of cross-bedding; and just below the upper white quartzite. In east- 

 central New York it is found at the base of the Oneida conglomerate, 

 which is the approximate equivalent of the upper white sandstone of 

 Niagara. In the Appalachians, it is found mostly in the upper part of 

 the Tuscarora and Clinch sandstones, the stratigraphic equivalent of 

 the Medina. Sarle' has recently interpreted this structure as due 

 to worm borings. So far as I have observed in the field, the raised 

 ridges of this fossil always occur on the under side of the sandstone 

 layers, representing, therefore, the relief molds of grooves generally 

 formed in the clays beneath. These grooves had a median ridge and 

 a regular succession of transverse ridges separated by broad concave 

 grooves. A similar structure, known as Climatichnites trails, but of 

 a much broader type, occurs in the Potsdam sandstone of New York. 

 Woodworth^ has suggested that it represents the trail of an animal 

 comparable to some extent to modern Chiton. 



There are no known remains of organisms in the Medina or 

 Clinton capable of making such an impression, and the organism 

 which made it either had no parts capable of preservation or else 

 it was a terrestrial type frequenting the shores and sandy wastes, 

 where it left its trail in the mud, but not its remains, just as the 

 Triassic Dinosaurs left their footprints but seldom their skeletons. 



The Tuscarora has a thickness of 820 feet in I^ogan's Gap, Jack's 

 Mountain, Mifflin County, Pennsylvania, but thins perceptibly west- 

 ward and southward, being 400 to 500 feet thick in Bald Eagle 

 Mountain and 287 feet in Wells Mountain and the Pennsylvania- 

 Maryland line. This thinning appears to be due to failure of the 

 lower beds, showing a true case of non-marine progressive overlap. 

 In New York, the upper part is represented by the true Medina, 

 which has a thickness of 125 feet, and begins and ends with a pure 

 white quartz sandstone. More strictly speaking, the upper white 

 sandstone alone represents the true Tuscarora, but the lower beds, 

 still partly red, and the shales, probably are the equivalent of the lower 

 reddish sandstones and greenish shales underlying the true white 

 Tuscarora, and sometimes referred to the Upper Juniata. The 

 Oneida conglomerate of central New York, 40 feet thick, is likewise 



1 Rochester Acad, of Sci. Proc, 1906, No. 4, p. 203. 



2 New York State Pal. Rep., 1907, Bull. New York State Museum, No. 6g, p. 959. 



