64 THE STORY OF THE EARTH. 



provinces occupy changed areas of the earth's 

 surface, with alterations in the level of land. 



In the same way it was found that life in the 

 Bea varies with the depth of the water. Sea-shells 

 which live between tide-marks, and are adapted 

 to e\i>t more or less exposed in atmospheric air, 

 are different in genera or species to those in the 

 deeper water, where the great growths of sea 

 plants are found. Marine life again changes its 

 character with greater depth. The shells which 

 would he indicative of a shore, travel along the 

 shore; and the shells which are found in clavs, 

 are rarely met with in sand. Marine life also 

 varie> geographically in the horizontal direction, 

 because there are natural history provinces of life 

 in the sea, which may also change their area, 

 when the depth of water changes, so as to scatter 

 or concentrate or combine the life. 



About the year [864 it began to be urged that 

 the differences found in the fossil life between 

 two successive geological deposits, were not due 

 to great denudations of intervening strata, which 

 had removed the intervening transitional organ- 

 isms, making breaks in the geological record, but 

 were the results of geographical migrations of 



inisms, so that these animals and plants came 

 into an area which they had not previously occu- 

 pied, by moving away from one which had for- 

 merly been their home. When fossilized, the 

 remains <.f such a group indicate a different as« 



Bemi I animals or plants to those which 



lived previously m the area, when the life in the 



und( imulated and was fossilized 



in the -.line way. 



Thus it is intelligible that the distribution of 

 life in the strata has been brOUghl about in the 



