AXMVEKSAEY ADDRESS OF THE PRESIDENT. 



xlv 



The conformity of which wo here speak is sometimes of such a 

 land as to bo expressed by the term " identity of species," more 

 frequently by the near resemblance of forms in the same genus, for 

 which the name of " representative species " has been employed by 

 E. Forbes. The term species is and must remain somewhat am- 

 biguous in palaeontology while the observers of different regions 

 prefer the inglorious task of inventing new names for their native 

 fossils, instead of the useful labour of a strict comparison of them 

 with sufficient examples of the species already described by foreign 

 naturalists. But there is seldom any ambiguity in a generic term ; 

 and in each region Ave can at least count the specific forms, or what 

 are considered to be such. This being done, we gain at onco a 

 power of numerical expression for the several groups which compose 

 the system of life of each period in each region, or what is preserved 

 of each system, and a representation of the associated life, inde- 

 pendent of the particidar determinations of the specific elements. 



Let us see the effect of such a method tried, in the systems of 

 strata in Britain, on the invertebrate groups of marine life. Taking 

 1000 for the sum of the species, and confining our computations to 

 large groups including several or many genera and species, wo 

 obtain the following tabular numbers %, which represent the propor- 

 tionate prevalence of each of the selected classes in each great 

 selected period. 



Zooph 



Echin. 



Crust. 



Brack 



Mon. 



Dim. 



Gast. I Ceph. 



Eocene 



Cretaceous 



Oolitic and Triassic . 

 Permian and Car 



boniferous 



Devonian 



Silurian and Cam 



brian 



35 



55 



107 

 »167 



157 



28 

 *163 



70 



116 



54 



04 



13 

 53 



15 



33 



38 



*1G8 



3 

 80 

 74 



173 

 »t302 



1-237 



*166 

 126 



105 



54 



44 



t213 



t340 



151 

 90 



116 



*t578 

 125 

 212 



tl78 

 140 I 



110 



10 

 165 



•190 



126 

 143 



103 



[Asterisks are affixed to the numbers which are maxima in each olaee ; t indi- 

 cates most abundant group in each system.] 



The preceding Table and Che annexed Diagram represent to the 



eye the relative prevalence of the several classes selected, in the 

 systems of strata named. 



^ Physiological Bt latin, is. 



Among the laws which appear mod general as guiding the 

 relations of living beings, is that which expresses the reciprocal 

 dependence of animals and vegetables upon the atmosphere. Every 

 plant and every animal depends apon the free atmosphere, or upon 

 the atmospheric elements absorbed by water; but this dependence 



I The numbers in each group maybe taken from B£oma> Catalogue, equating 

 the sum to 1000. Thia method was much employed by me in "oHAPtang the 

 results of my surveys in I ».-\ . .n-liir.- (1839, Ac.), for the Falajoaoic fosrila of thai 

 county (1841) ; again in the Bfemoin "t" the Gtol. Surrey, MalYernia (1844 



and in my Guide and Manual of Qeology (1834 1 855), 



