FOSSIL TRACKS IN THE DEL RIO CLAY. 
J. A. Udden, Ph. D.* 
While examining the Del Eio clay in its typical exposures in the 
bluffs south and east of Del Rio in Texas three years ago, I found some 
tracks in layers of a fine sandstone which occur at a distance of about 
forty feet below the Buda limestone. The latter rock has been eroded 
away from the edge of the bluff, but it is apparently not very far away 
to the southeast, and loose boulders of it occur on top of a hill south* 
of the town of Del Rio. A well is reported to have gone down through 
more than 200 feet of clay, and this is the minimum thickness of the 
formation in this locality. A considerable part of the clay is red from 
the presence of oxide of iron. The uppermost twenty feet of the forma- 
tion contains calcareous layers, in which Exogyra arietina and Nodosaria 
texana are profuse. Sandy layers occur farther down and attain a 
thickness from six inches to a foot. They show occasional ripple marks, 
and in places they were seen to occupy small erosional hollows in the 
underlying clay. They consist of fine and clean sand, apparently sorted 
by repeated washing during the transportation on the old sea bottom. 
These ledges, which contain the tracks, are evenly laminated and the 
laminae are notably straight, weathering occasionally in thin plates. 
The tracks consist of two rows of oval depressions, the distance be- 
tween the center of the two rows being about half an inch, and the 
distance between two successive depressions in the same line being a 
little less. They are represented in the accompanying Figure 1, which is 
a photograph of one of the specimens secured. Several specimens were 
noted, and for some distance in the exposed ledge they could be found 
at a particular level in the rock. They bear a perfect resemblance to 
tracks made in sand by small crawfish, and it may deserve notice that 
small iragments of decapods are occasionally found in the Del Rio 
formation, though they were not noticed in this locality. 
Another locality where I noted the same tracks was in the bed of 
Sycamore creek, at its forks near the northwest corner of survey No. 6, 
in block 5 of the International & Great Northern Railroad lands in 
Kinney county. 
In the same sandy layers at various localities I observed another 
kind of markings, which I ascribe to the formation of ice crystals on 
muddy flats. These consist of branching patterns of straight lines 
usually from one to six inches in length. A slab with imperfect speci- 
*Professor of Geology, Augustana College, Rock Island, Illinois. 
