OF CREATION. 389 



among the most widely extended groups, constantly 

 represented in closely allied, if not identical specific 

 forms. In other words, they are the most cosmo- 

 politan of existing Mollusca ; they are gregarious and 

 often live in great depths of water, but lastly they 

 have considerable vertical range, and are greatly 

 similar to one another in their development in time. 

 Some, no doubt, of the highest Mollusca, nearly re- 

 lated to the common squid or cuttle-fish, are also very 

 widely spread, but this arises from the free-swimming 

 habits of the animal, and is therefore to be considered 

 as having a different cause from that which obtains in 

 the former case, where the animal, at least in the full- 

 grown state, is permanently attached to some subma- 

 rine body. 



No animals, again, at the present day, are more 

 widely distributed than those which secrete and de- 

 posit in various ways solid calcareous matter; and of 

 all these it would be difficult to find any that have 

 greater influence than some of the smaller zoophytes. 

 It is just these animals also whose remains are distri- 

 buted through rocks of various ages, and which, there- 

 fore, seem to determine least effectually, in time as 

 well as space, any important point with regard to the 

 true geological position of a containing rock. 



If, leaving the Invertebrata, we examine the various 

 groups of vertebrate animals, a nearly similar result 

 is obtained. Certain groups of fishes now charac- 

 terise certain limited districts, and this without our 

 being able to discover any reason for it. Of these 

 groups some exhibit much higher organization than 

 others, arid present marked differences of habit and 

 structure, while some, on the other hand, are more 



