61 
upper part of the canyon. In some cases the imprints are on thin-bedded, 
ripple-marked sandstone, whereas in other cases they are on massive, 
clay-ironstone beds. In places upright stems or roots of plants are very 
numerous in the stratum on which the tracks are preserved. Many of the 
clay beds show mud-cracks. On some of the strata tracks are quite 
numerous, whereas at other horizons only an occasional imprint is visible, 
but as the exposed area of many of the horizons is small no significance may 
be attached to this condition. Several long trackways are visible and 
along some of these the character of the surface or the indicated speed of 
travel of the animal is quite different at the two ends of a trackway. 
In the early days of the study of fossil footprints, species were some- 
times described which differed from other species mainly or solely in size of 
imprint, length of stride, and width of trackway. Study of the Peace 
River tracks seems to show that these characters alone are not always 
diagnostic. Though a great difference in size may as a rule be sufficient 
reason for specific differentiation, yet the tracks of one species about to be 
described vary from 11 to 16 inches in length. Although a relatively 
long stride does, of course, indicate a long-legged animal, it is also true that 
the length of stride and the width of trackway have a definite relation both 
to the speed of travel of the animal and to the nature of the travelled surface. 
In several trackways at horizons below the Grant seam (Gcthing’s mine), 
Peace River canyon, the mud was so soft that the dinosaur sank deeply 
into it and -when the foot was withdrawn the mud so closed in that only 
saucer-like depressions remained. In these trackways the tracks are wide 
apart and the stride much shorter than is usual where the surface was more 
solid. In one trackway (See Figure 5) the stride progressively shortens 
from 31 to 27 inches. In another trackway of the same species and size of 
track, the stride is only 21 inches. In still another trackway, consisting of 
sixteen imprints, the tracks for the greater part of the trackway are in 
almost a direct line and the average stride is 37 inches. Three of the 
imprints, however, indicate a rather sudden stopping, and there the track- 
way is wider and the stride only 26f inches (See Plate II). 
SYSTEMATIC DESCRIPTIONS 
Some early students attempted to correlate footprints with the osseous 
remains, but Hay 1 and Lull 2 study tracks without attempting to correlate 
species of tracks with species of animals, even where they are quite confident 
as to which animal made the tracks. The latter course is the better, for 
seldom can one be certain of the nature of the animal that made the tracks. 
In fact in the case of dinosaur tracks it is not always certain to which ordei 
of dinosaurs the animal that made the tracks belongs. Lull proposed 
(Loc. cit.) eight families to include the Connecticut Valley ichnites. It 
seems unwise, at this time, to propose more new families than are absolutely 
necessary and, therefore, in the following account most of the genera are 
tentatively referred to one or another of Lull’s families, though it is fully 
recognized that in some cases they do not entirely correspond with the 
family characters as given by Lull. 
"Hay, O. P.: U.S. Geol. Surv., Bull. 179, p. 538 (1902). 
•Lull, R. S.: Mem. Boston Soc. Nat. Hist., vol. 5, pp. 461-557 (1904); State Geol., Nat. Hist. Su v.. Conn. 
Bull 24, p. 173 (1915). 
