PAC Tie eee eV ele 
CASTS OF TRAILS AND MARKINGS (p. 63). 
Fias. 1, 2. Casts of trails made on sand and silt by alge, drifting with the outflowing tide, at 
inlet west of Noyes Point, Rhode Island. For comparison with fig. 3 of this plate and 
figs. 1 and 4 of Pl. XXXVII. (Photograph by C. D. W.) 
Fic. 3. Cast of trails on Middle Cambrian sandstone 5 miles southwest of Rogersville, Tennessee. 
(Collection United States National Museum. ) 
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