324 MARKINGS, FOOTPRINTS AND FUCOIDS 



vertebrate animals having limbs, the information we can obtain 

 is of a far more definite character. This has already been re- 

 ferred to in treating of the first Air-breathers in a previous 

 chapter. One very curious example we may close with. It is 

 that of the celebrated " bird tracks " of the sandstone quarries 

 in the Trias of Connecticut and Massachusetts. These tracks, 

 of immense size, as much as eighteen inches in length, and so 

 arranged as to indicate the stride of a long-legged biped, were 

 naturally referred to gigantic birds, allied to modern waders. 

 But when it was found that some of them showed a central 

 furrow indicating a long tail trailing behind, this conclusion was 

 shaken, and when in tracing them along, places were found 

 where the animal had sat down on its haunches and the end of 

 its tail, and had brought down to the ground a pair of small fore 

 feet with four or five fingers, it was discovered that we had to 

 deal with biped reptiles ; and when the tracks were correlated 

 with the bones of the extinct reptiles known as Dinosaurs, we 

 found ourselves in the presence of a group of the most strange 

 and portentous reptilian forms that the earth has ever known. 

 Marsh has been enabled, by nearly perfect skeletons of some 

 allied reptilian bipeds found in the West, to reproduce them 

 in their exact forms and proportions, so that we can realize in 

 imagination their aspect, their gait, and their gigantic propor- 

 tions. Examples of this putting together of footprints and 

 osseous remains of vertebrate animals are not rare in the 

 history of geology, and show us how the monsters of the 

 ancient world, equally with their human successors, could leave 

 " footprints on the sands of time." 



The Dinosaurs which have left their footprints on the sand- 

 stones of Connecticut and Massachusetts are, however, greatly 

 more numerous than those known to us by osseous remains. 

 Thus footprints have the further use of filling up the imperfec- 

 tions of our geological record, or at least of pointing out gaps 

 which but for them we might not have suspected. The re- 



