nil \\I-M AND USE OF FOSSILS 87 



living terrestrial vegetation be dredged op from 



refore, marine forms of life must be taken 

 as evidence of the pretence of the iea and terrestrial 

 forms as proof* of land, these furnish us with an easily 

 able and reliable test of change of level between 

 sea and land, as well as a measure of its minimum amount. 

 A natural terrace of sand and gravel, full of littoral shells. 



and extending along a coast- line at a height of 100 feet 

 above the present sea-level, shows that sea and land have 

 1 relatively to each other to the extent of at least 

 too feet Geologists are not all agreed as to whether in 

 such changes of K- the land or the sea which 



moves up or down. Where evidence can be obtained 

 of marked local variations in the amount of change it is 



may of coone occur where close to the 

 margin of the land fresh-water lakes may be entered by the sea, and 

 there may be a partial commingling of marine and fresh -water 

 organisms. But such examples will seldom lead to any mistake. 

 For an interesting account of one illustration of this mixture of the 

 life of fresh and salt water, see Hugh Miller's AW/WM/J of tk< 

 Crmtrr, chap. L Again, where portions of the sea hare been 

 isolated and carried upward on an upraised surface of land, so as to 

 become inland lakes, marine types of life may in the course of ages 

 survive and undergo modification as denizen* of fresh water. The 

 fauna of some of the African lakes may be cited in illustration. 



