210 NATURAL HISTORY. 



'zones of depth,' each characterised by particular types 

 of animals. 



The first of these zones is the so-called ' littoral zone,' 

 embracing the tract between tidemarks, and characterised, 

 not only by its abundant development of different kinds 

 of seaweeds, but also by a number of peculiar animals. 

 The littoral animals must be capable of being left 

 uncovered twice a day by the receding tide, and they 

 must also be able to withstand exposure to the direct rays 

 of the sun. Hence, the animals of the littoral zone are 

 mostly referable to peculiar types ; and the same types, or 

 'representative' types, are found between tide-marks in 

 almost all parts of the world. 



Below low-water mark, and extending to the depth of 

 about fifteen fathoms, is what is known as the ' laminarian 

 zone,' so called from the abundance in it of the great 

 strap-like ' tangle ' (Laminaria). The fronds of this sea- 

 weed form a sort of submarine forest in the shallow 

 water all round our coasts, the upper edge of which is 

 just visible at the lowest ebb of the spring-tides ; and it 

 affords shelter and food to a vast abundance of marine 

 animals. Many of the species of the laminarian zone are 

 peculiar, and they are often remarkable for the brilliancy 

 of their coloration. 



A third zone was termed by Forbes the ' coralline zone,' 

 and it extends from about fifteen fathoms to fifty fathoms 

 in depth. In this zone, plants are chiefly represented by 

 the peculiar coral-like calcareous Algce known as the 

 ' Corallines ' and ' Nullipores.' Animal life is extremely 

 abundant, and many of the species are peculiar. 



Lastly, Forbes recognised a fourth or 'deep-sea coral 



