GEADUATED SERIES OF FOSSIL SPECIES. 3 1 



even now they cause the greatest perplexity and occasion 

 endless disputes among systematic palaeontologists about the 

 arbitrary limits of species. 



An excellent example of this is furnished by the celebrated 

 and very variable fresh- water snail from the Stuben Valley, 

 near Steinheim, in Wlirtemburg, which has been described 

 sometimes as Paludina, sometimes as Valvata,eiiid sometimes 

 as Planorbis Tnultiformis. The snow-white shells of these 

 small snails constitute more than half of the mass of the 

 tertiary limestone hills, and in this one locality show such an 

 astonishing variety of forms, that the most divergent extremes 

 might be referred to at least twenty entirely different species. 

 But all these extreme forms are united by such innumerable 

 intermediate forms, and they lie so regularly above and 

 beside one another, that Hilgendorf was able, in the clearest 

 manner, to unravel the pedigree of the whole group of 

 forms. In like manner, among very many other fossil 

 species (for example, many ammonites, terebratulae, sea 

 urchins, lily encrinites, etc.) there are such masses of con- 

 necting intermediate forms, that they reduce the " dealers 

 in fossil species " to despair. 



When we weigh all the circumstances here mentioned, 

 the number of which might easily be increased, it does 

 not appear astonishing that the natural accounts or 

 records of creation formed by petrifactions are extremely 

 defective and incomplete. But nevertheless, the petrifactions 

 actually discovered are of the greatest value. Their signifi- 

 cance is of no less importance to the natural history of 

 creation than the celebrated inscription on the Rosetta 

 stone, and the decree of Canopus, are to the history of 

 nations — to archaeology and philology. Just as it has 



