PLATE XXXVIT. 
CASTS OF TRAILS AND MARKINGS (pp. 62, 63). 
Fic. 1. Casts of trails on Middle Cambrian sandstone 4 miles northeast of Rogersville, Tennessee. 
These trails show an apparent bifurcation, and also a raised margin, indicating an elevated 
center. This feature is shown by the trails produced by alge, fig. 1 of Pl. XXXVI. 
(Collection United States National Museum. ) 
Fig. 2. Cast of trail having coarse parallel striz, on the surface of the Middle Cambrian (Tonto) 
sandstone, Grand Canyon of the Colorado, Arizona. (Collection United States National 
Museum. ) 
Fic. 3. Slab of sandstone from same locality as that shown in fig. 1. showing Eophyton-like trails 
ataandb. The trail at a is coarse, like a of fig. 2 of Pl. XXXII. The strive at b are very 
fine, like those of fig. 1 of Pl. XXXII. 
Fic. 4. Cast of fine trails on surface of shaly (Middle Cambrian) sandstone 10 miles east of Knox- 
ville, Tennessee. These striz are somewhat similar to those illustrated by Nathorst, 
which he suggested might have been produced by the tentacles of medusze. 
