chap, i.] PHYSICAL GEOGRAPHY. 15 



of life which inhabit that surface have, during every 

 period of which we possess any record, been also slowly 

 changing. 



It is not now necessary to say anything about how 

 either of those changes took place ; as to that, opinions 

 may differ ; but as to the fact that the changes themselves 

 have occurred, from the earliest geological ages down to 

 the present day, and are still going on, there is no dif- 

 ference of opinion. Every successive stratum of sedi- 

 mentary rock, sand, or gravel, is a proof that changes of 

 level have taken place ; and the different species of animals 

 and plants, whose remains are found in these deposits, 

 prove that corresponding changes did occur in the organic 

 world. 



Taking, therefore, these two series of changes for granted, 

 most of the present peculiarities and anomalies in the 

 distribution of species may be directly traced to them. In 

 our own islands, with a very few trifling exceptions, every 

 quadruped, bird, reptile, insect, and plant, is found also 

 on the adjacent continent. In the small islands of Sar- 

 dinia and Corsica, there are some quadrupeds and insects, 

 and many plants, quite peculiar. In Ceylon, more closely 

 connected to India than Britain is to Europe, many 

 animals and plants are different from those found in India, 

 and peculiar to the island. In the Galapagos Islands, 

 almost every indigenous living thing is peculiar to them, 



