1522 THE STORY OF THE UNIVERSE 



The life-forms of these zones vary, of course, ac- 

 cording to the nature of the sea bottom; and are 

 modified by those primitive or creative laws that 

 have caused representative species in distant localities 

 under like physical conditions species related by 

 analogy. 



Very much remains to be observed and studied by 

 naturalists in different parts of the globe, under the 

 guidance of the generalizations thus sketched out, 

 to the completion of a perfect theory. But in the 

 progress to this, the results can not fail to be prac- 

 tically most valuable. A shell or a sea-weed, whose 

 relations to depth are thus understood, may afford 

 important information or warning to the navigator. 

 To the geologist the distribution of marine life ac- 

 cording to the zones of depth has given the clew to 

 the determination of the depth of the seas in which 

 certain formations have been deposited. 



By the light of these laws of geographical distri- 

 bution we view with quite a new interest the shells, 

 corals, and sea-weeds of our own shores. We trace 

 the regions whence they have been invaded by races 

 not aboriginally belonging to our seas; we obtain 

 indications of irruptions of sea-currents of dates an- 

 terior to the present arrangements of land and water. 

 Thus, part of our marine fauna has been traced back 

 to the old Pliocene period, part to the somewhat 

 newer period of the red-crag, part to the still more 

 recent glacial period all these being anterior to 

 the constitution of the Celtic Province, as it is now 

 displayed. 



The class of animals to which the restrictive laws 



