PLATE XXXVII. 



Casts of trails and markings (pp. 62,63). 



Fig. 1. Casts of trails on Middle Cambrian sandstone 4 miles northeast of Kogersville, 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 alga?, fig. 1 of PI. XXXVI. 



(Collection United States National Museum.) 

 Fig. 2. Cast of trail having coarse parallel stria?, on the surface of the Middle Cambrian (Tonto) 



sandstone, Grand Canyon of the Colorado, Arizona. (Collection United States National 



Museum.) 

 Fig. 3. Slab of sandstone from same locality as that shown in fig. 1. showing Eophyton-like trails 



at a and b. The trail at <t is coarse, like a of fig. 2 of PI. XXXII. The stria? at b are very 



fine, like those of fig. 1 of PI. XXXII. 

 Fig. 4. Cast of fine trails on surface of shaly (Middle Cambrian) sandstone 10 miles east of Knox- 



ville, Tennessee. These stria? are somewhat similar to those illustrated by Nathorst, 



which he suggested might have been produced by the tentacles of medusa?. 



178 



