THE FERNS OF SUTHERLAND AND ROSS. 29 



After the Mollusca asra appeared the Vertebrate class, of which the four 

 great divisions, Fishes, Reptiles, Birds, and Quadrupeds, are organized 

 according to one type. This was the Devonian Period, with which the 

 Silurian is included in the age of Algae, or of sea-weeds. 



The Ganoid tribe of Fishes now existed, and continued till the middle 

 of the Reptilian Age. The earliest Fishes having the most perfect organ- 

 ization, almost all passed away, and were succeeded by other kinds. The 

 species of Fishes before mentioned being exterminated, the epoch of Am- 

 phibians and of Coal Plants, or the Carboniferous Age ensued. The lower 

 division of Reptiles, such as the tribe of Frogs and of Salamanders, and 

 those of immense size, now took the load. These are most allied to Fishes, 

 having gills when young. 



Land had now appeared, and when the Amphibians flourished, the land 

 plants were first in exuberant growth, and by cleansing the atmosphere 

 from carbonic acid, made it suitable for the respiration of land animals. 

 These plants (flowerless trees or Acrogens) and Coniferae then disappeared, 

 and the last Lepidodendra lived in the forests of the Carboniferous con- 

 tinents. 



The Amphibians comparatively passed away, and the age of true Reptiles 

 gradually appeared in all its grandeur. Reptiles larger than Whales in- 

 habited the water, immense reptiles were on the land, and flying Reptiles 

 in the air. But they began to decline before the close of the epoch, and 

 the last flying Reptile and swimming Saurian existed in the Reptilian Age. 



Thus the Mollusca, the Fishes, and the Reptiles successively passed their 

 prime, and dwindled both as to number of individuals and as to rank of 

 species. Each of these great epochs contained many lesser periods, in each 

 of which there are subordinate examples of the law of degradation. The 

 Mollusca, with their companions, the Corals, the Crinoids, and the Trilobites, 

 were either wholly or more frequently partially exterminated, and were 

 replaced by new kinds, and the same may be said of the Fishes and of 

 the Reptiles, and the causes of such disturbances can be often traced. The 

 age of Reptiles includes the periods between the Coal epoch and the Ter- 

 tiary epoch. 



(To be continued.) 



A PEEP AT THE 

 FERNS, ETC., OF SUTHERLAND AND ROSS. 



BY W. 

 ( Continued from page 13. ) 



Aftkr exploring, to the best of my ability, the country round Durness, 

 I resolved on an expedition to Cape Wrath. In company with the minister 



VOL. VII. f 



