226 A CENTURY OF SCIENCE 



Hitchcock's conception of the track-makers was more 

 or less imperfect because of the fact that for a long time 

 but a few fragmentary osseous remains were known, 

 either directly or indirectly associated with the tracks, 

 while on the other hand the bird-like character of many 

 of the latter and the discovery of huge flightless birds 

 elsewhere on the globe suggested a very close analogy if 

 not a direct relationship. Hence "bird tracks " they 

 were straightway called, a designation which it has been 

 difficult to remove, even though in 1843 Owen called atten- 

 tion to the need of caution in assuming the existence of 

 so highly organized birds at so early a period, especially 

 when large reptiles were known which might readily 

 form very similar tracks. The footprints are now 

 believed to be very largely of dinosaurian origin, and 

 dinosaurs whose feet corresponded in every detail with 

 the footprints have actually come to light within the same 

 geologic and geographic limitations. This of course 

 refers to the bipedal, functionally three-toed tracks. Of 

 the makers of certain of the obscurer of the quadrupedal 

 trails ^we are as much in the dark to-day as were the 

 first discoverers of a century ago, so far as demonstrable 

 proof is concerned. We assume, however, that they were 

 the tracks of amphibia and reptiles, beyond which we may 

 not go with certainty. 



Agassiz, writing in 1865 (Geological Sketches), says: 



"To sum up my opinion respecting these footmarks, I believe 

 that they were made by animals of a prophetic type, belonging 

 to the class of reptiles, and exhibiting many synthetic charac- 

 ters. The more closely we study past creations, the more 

 impressive and significant do the synthetic types, presenting 

 features of the higher classes under the guise of the lower ones, 

 become. They hold the promise of the future. As the opening 

 overture of an opera contains all the musical elements to be 

 therein developed, so this living prelude of the creative work 

 comprises all the organic elements to be successively developed 

 in the course of time." 



Of those whose work was contemporaneous with that 

 of Hitchcock, but one, W. C. Redfield, wrote on Triassic 

 phenomena, and he concerned himself mainly with the 

 fossil fishes of that time, his first paper on this subject 



