400 



HISTORICAL GEOLOGY 



passed. Large alligatorlike forms of powerful build were still 

 common in the Triassic marshes, but after this period the class 



was represented only by 

 smaller soft-bodied types, 

 such as frogs and salaman- 

 . ders. 



The reptiles were the class 

 $| in power. The bones of 

 many reptiles have been 

 If found hi the Triassic rocks, 

 / and the existence of others is 

 made known to us by the 

 host of footprints (Fig. 420) 

 which they left upon the 

 muddy flats along the slack 



FIG. 419. One of the simpler ammo- rivers and ba y s > ** m the 

 nites (Ceratites) showing the moder- valley of the Connecticut 

 ately folded sutures. T, rni i i 



River. The mud has since 



hardened into stone, but without effacing the footprints. 

 Some of these tracks show the marks of three toes, and were 

 at first very naturally mistaken for those of birds. 



FIG. 420. Tracks of three-toed reptiles found in the Triassic sandstone of 

 , the Connecticut Valley. (After Hitchcock.) 



