OF CREATION. 45 



peculiarities of structure. Some of them appear to 

 have been of great length and exceedingly slender ; 

 and the shell is often thin, although in that case the 

 walls of separation between each two successive 

 chambers are generally close together. The sides of 

 the shell are often deeply ribbed or grooved, some- 

 times in the direction of its length, and sometimes 

 across. A few of the species had their shells short and 

 greatly swelled, having almost the shape of a pear ; 

 some again came rapidly to a pointed termination ; 

 and some were so nearly cylindrical, that it is difficult 

 to suppose that they ever commenced at a point, and 

 were increased by regular gradations. All these va- 

 rieties of form are met with in the oldest rocks ; and 

 the large and important group of Orthoceratites, 

 apparently the first, as it is the simplest form of 

 the multilocular shell, seems to have attained its 

 greatest development very early, and then was gra- 

 dually replaced by other groups of Cephalopoda; until, 

 towards the close of the first epoch, these animals 

 had died out entirely, and were replaced by the 

 nautilus, and yet more remarkably by the ammo- 

 nites, which then appeared for the first time. 



We have now gone through the description of the 

 inhabitants of the seas during the earliest period at 

 which the Geologist is enabled to trace the existence 

 of living beings upon the earth. Let us, before con- 

 cluding, briefly reconsider the results of geological 

 investigation with regard to these ancient strata. 

 In the first place, it is interesting to remark, that, 

 among the groups exhibiting the lowest amount of or- 

 ganization, there are a few corallines, and a larger num- 

 ber of the stony corals. There are also several species 



