82 Dynamic Theory. 



seous fishes are derived from an ancestor that was also ancestor to the 

 Ganoid, and more remotely from an ancestor that was ancestor to the 

 Selachian, yet it is very evident that after the separation of these fam- 

 ilies from the Teliosts, both of them took on characteristics that after- 

 wards appeared in the Reptiles. It would indicate that the original 

 stock also contained the reptile element, and that the Reptile is a branch 

 taken off the main stem, close to its junction with the Placoid. The 

 features alluded to are these : The eggs of some of the Sharks of the 

 present time are impregnated in the ovary of the mother. They are 

 few in number, large and well covered, like those of some reptiles and 

 birds. Other Sharks hatch the eggs and bring forth the young alive, as 

 some reptiles do. ' ' In some cases there is even an attachment between 

 the yolk sac of the internally hatched young and the oviduct of the 

 mother, somewhat similar to that of the placenta to the uterus of the 

 mammal. The } r oung of Placoids, also, at first have a kind of external 

 branchiae ( gills ) like those of amphibian reptiles. " ( LeConte's Geology 

 331.) The Ganoids, on the other hand, possess the armor teeth, swim- 

 bladder, paired fins and tail fin of the lower reptiles. 



CHAPTER XL 



CARBONIFEROUS COAL, AGE. 



This age is distinguished by the luxuriance of its vegetation, which 

 it laid down in vast strata in many places, and the consolidation of 

 which, under pressure, gives us our coal. The age is classed as Paleo- 

 zoic, by the geologists, because its features, of both animal and vegeta- 

 ble life, remain, in general, the same as of old, and distinguish this and 

 preceding ages from those which follow. 



By this time a considerable portion of the earth's crust had become 

 raised above the water, and land plants had an opportunity to flourish. 

 The vegetation became rank and large compared with that of the same 

 families of the present time in the same latitudes. There is a continua- 

 tion of the sea-weeds. The land plants represented were chiefly Aero- 

 gens Ferns, Lycopodia or Ground Pines, Equiseta and Calamites. 

 These are of a low order Botanically, but they made up in size what 

 they lacked in organization. The ferns we see now are only three or 

 four feet high. But then they sometimes grew in the United States as 

 they do now in the tropics, a bunch of leaves on the top of a tree stock 

 many feet high. The Lycopodia were then sixty to eighty feet high, 

 now they are mere shrubs. The common scouring rush is a modern 

 Equisetum, but in the Carboniferous age the Calamite, which has been 

 classed by some as an Equisetum, was thirty feet high and two feet in 



