A HISTORY OF SCIENCE 



gion hitherto geologically explored. These records were 

 made known mainly by Professors Joseph Leidy, O. C. 

 Marsh, and E. D. Cope, working independently, and 

 more recently by numerous younger paleontologists. 



The profusion of vertebrate remains thus brought to 

 light quite beggars all previous exhibits in point of mere 

 numbers. Professor Marsh, for example, who was first 

 in the field, found three hundred new tertiary species 

 between the years 1870 and 1876. Meanwhile, in 

 cretaceous strata, he unearthed remains of about two 

 hundred birds with teeth, six hundred pterodactyls, 

 or flying dragons, some with a spread of wings of twen- 

 ty-five feet, and one thousand five hundred mosasaurs 

 of the sea-serpent type, some of them sixty feet or more 

 in length. In a single bed of Jurassic rock, not larger 

 than a good-sized lecture-room, he found the remains 

 of one hundred and sixty individuals of mammals, rep- 

 resenting twenty species and nine genera; while beds 

 of the same age have yielded three hundred reptiles, 

 varying from the size of a rabbit to sixty or eighty feet 

 in length. 



But the chief interest of these fossils from the West is 

 not their number but their nature ; for among them are 

 numerous illustrations of just such intermediate types 

 of organisms as must have existed in the past if the 

 succession of life on the globe has been an unbroken 

 lineal succession. Here are reptiles with bat-like wings, 

 and others with bird-like pelves and legs adapted for 

 bipedal locomotion. Here are birds with teeth, and 

 other reptilian characters. In short, what with rep- 

 tilian birds and birdlike reptiles, the gap between 

 modern reptiles and birds is quite bridged over. In a 



106 



