PROGRESS OF LIFE. 601 



world was probably well peopled with them, (c.) Again, the Car- 

 boniferous age left testimony as to the kinds of vegetation that grew 

 about and in its great marshes. But it affords nothing with re- 

 gard to the forests that covered the higher parts of the continent 

 in its higher latitudes, or west of the 100th meridian. Again, in the 

 Triassic and Jurassic periods, the land was, we cannot doubt, as abun- 

 dantly covered with vegetation as in the Carboniferous age ; and yet 

 we have only a very meagre record from the American rocks, and one 

 but little better from those of Europe, (d.) The Jurassic period in 

 Europe must have had in every part its numerous Birds ; and yet we 

 know them, thus far, only from the discovery of one single specimen 

 at Solenhofen. 



A broken record the geological undoubtedly is, especially for ter- 

 restial life. The marine life, particularly that of the Paleozoic, is 

 better displayed ; since marine formations were then more extensively 

 in progress over the Continental seas than later ; and the life of the 

 world was also much alike in the two hemispheres. 



Such facts invalidate the force of geological testimony, but without 

 proving that abruptness of transition was not still a general fact. 



(e.) The force of the evidence is further weakened by discoveries 

 made from time to time, that diminish some of the wider gaps among 

 the abrupt transitions. Thus, the Horse, an animal with one large toe 

 making the whole foot, and no relics of other toes, excepting two 

 slender bones either side, — called the splint-bones, — has been found 

 (as shown on page 507) to have been preceded in Tertiary times by 

 other Horses, with real toes in place of the splint-bones ; and thus a 

 transition has been made out toward related animals with a foot of 

 four or five toes. Again, the Birds, now standing apart so stiffly, as 

 animals with bills and feathers and short tails, in former times had 

 teeth in their jaws (p. 466), and long tails (p. 446), and, moreover, in 

 the Reptilian age, there were biped Reptiles, with the hollow bones 

 and some other characteristics of Birds (p. 414). 



Arctic America contains, in Tertiary fossils, remains of plants so 

 much like species existing in the forests of both temperate North 

 America and Europe (p. 526), that the former have been pronounced 

 the undoubted progenitors of the latter. 



But, while such discoveries have been made in many directions, 

 they have still left, with rare exceptions, abrupt transitions between 

 genera or groups ; and in hardly a case in the animal kingdom have 

 they yet filled out all gradations. 



The admitted imperfections in geological history, owing to poor 

 records, and these not half consulted, lead the cautious geologist to 

 wait, before dogmatizing. 



