XXXIV PROCEEDINGS OE THE GEOLOGICAL SOCIETY, ; 



hinge-apparatus is similar, the internal supporting shelly loops are 

 similar, and the heak is similarly perforated. So Rhynchonella is 

 common in the Silurian, Devonian, Carboniferous, and Permian 

 rocks ; abounds in the Liassic, Oolitic, and Cretaceous ; but is hardly 

 known in the strata above, and is rare in the modern sea. A sur- 

 prising resemblance runs through all the groups, though, as in the 

 case of Terebratula, the fades differs in each of the great periods, 

 and, indeed, in the several systems in those periods. 



"Whoever considers these facts with attention and with good col-' 

 lections before him, can come to no other conclusion than that here 

 nearly the whole series of the forms of these genera is preserved to 

 us. The same conclusion is to be drawn from a study of Lingula 

 —a Cambrian and Silurian, but also a living genus, which has left 

 monuments in every group of strata, very little differing from the 

 recent examples. 



"When, then, we find the groups of the Orthis Spirifer, Leptcena, 

 Producta, and Pentamerus so remarkably terminated at this or that 

 level, we are not required to interpose at each of these levels an 

 enormous interval of time unrepresented by forms of life, any more 

 than such a supposition is countenanced by the first appearance of 

 these genera. These beginnings and endings have relation to the 

 peculiarities of each genus and each species, and to the influences on 

 each. "While Orihoceras died out, and Belemnites began and ended, 

 Ifautilus lived on, with characters but little altered, through the 

 Palaeozoic and all later times, and is still a living genus. So Tri* 

 gonia, beginning in the muschelkalk, maintains its place on the 

 Australian shore ; and PJioladomya, whose geological range is nearly 

 the same, has still a representative in the sea at Tortuga. 



One very important truth flows naturally from the examination 

 of such groups as RJiynchonella, Lingula, Pholadomya, and others 

 which have a long series of representatives in time. "While the 

 natural group existed, its main structural characters persisted, and 

 its essential habits of life remained similar in all the lapse of time ; 

 so that we may feel confidence in applying to a fossil group the 

 arguments founded on real and structural analogy with existing 

 races, 



P>y considering these and many other cases, it appears, with refer- 

 ence to the use we make of organic fossils in judging of the consti- 

 tution of ancient nature, that we are not without sufficient data to 

 determine the probable character of the atmosphere, and the probable 

 character of climate ; that we can trace the action of light on the 

 eyes of the primeval trilobite, in exciting the growth of coral, and in 

 tinting some of the shells ; that we can class the animal population 

 of every age according to its food, and thus, by just reasoning, 

 arrive at a conspectus of the state of the land and sea, which, though 

 incomplete, need not be regarded as erroneous. 



Finally, whatever degree of imperfection may still cling to our 

 collections of data, it is daily growing less and less by the world- 

 wide industry of our zealous workmen. Pew of the several periods 

 of geology have been left without some natural monuments of the 



