PALEONTOLOGY 



813 



Animal tracks may also be fossilized by being filled in with later de- 

 posits of sediment. When the deposits solidifj^ into rock, and are spht 



l 



^^ 



|i 



r^ 



Fig. 214. — Footprints of two dinosaurs (one large and one small) and rain-marks 

 preserved in a slab of Triassic sandstone. (From Schuchert's Historical Geology. Courtesy 

 of John Wiley and Sons.) 



apart, the lower stratum contains a mold, the upper one a cast, of the 

 animal's foot. Figure 214 represents such a foot-print. The marks of 

 raindrops in clay have been preserved in a similar manner (Fig. 215), but 



Fig. 215. — Natural casts of rain imprints and dinosaur tracks. (From Schuchert's Historicaj. 



Geology. Courtesy of John Wiley and Sojis.) 



since they are not animal remains it is questionable whether thej' should 

 be called fossils at all. Plant impressions are Hkewise very common, a 



