OF PLANORBIS AT STEINHEIM. 37 



Kraussii, and so on, which until now have been found in no other Tertiary formation, 

 astonishes one at first, and occasions one to overlook the manifold relations which exist 

 between the Steinheim fauna, that of the Upper Freshwater Molasse, and that of the 

 Sylvana Limestone, which (last) appears at Neuselhalder, under such circumstances that 

 it must at any rate be considered as the next oldest Tertiary formation of the neighbor- 

 hood." This opinion is supported by along list of all the fossils found in this and other 

 localities, and other remarks which will be quoted more fully hereafter. Prof. Sandberger 

 is an acknowledged authority upon the Tertiary shells of continental Europe, and this 

 opinion, therefore, is of the greatest weight, especially when it is accompanied, as in the 

 present case, by a wealth of illustration, and a detailed text which most fully supports the 

 position. 



Again the same authority does not describe the Neuselhalderhof rocks, under the 

 heading of Steinheim, but under that of the "Land und Siisswasser Conchylien des 

 Kalkes mit Helix sylvana, und der oberen Siisswasser Mollasse der Schweiz Schwabens 

 und Bayerns," and speaks of it as follows : " The Upper Miocene Limestone with Melix 

 sylvana again appears to the north-west of Ulm, first at Neuselhalderhof" (one hour 

 from Steinheim), and then describes its occurrence at a host of other places in various 

 parts of Germany, in scattered detached masses, the remnants of the former deposits of 

 an equally large number of fresh-water lakes of the Upper Miocene period. 



Though none of these authors state distinctly the relationship of the Sylvana Limestone 

 at Neuselhalder to other rocks or by what it is immediately underlaid, they all agree that 

 it must be a remnant of a former period and it contains as stated by Hilgendorf the 

 elements from which the shell fauna of the Steinheim lake-basin were in all probabiHty 

 directly derived. It is equally clear that it occupies according to Sandberger a position 

 underneath the Planorbis bed, a formation in which he found PL levis var. aequiwmbili- 

 catus Hlg. on the Neuselhalderhof road. 



These facts support the proposition advanced by Hilgendorf, that the ancestors of the 

 Planorbis forms of the Pits are found in the Fl. levis, var. aequiumbilicatus of the 

 Neuselhalder rocks. Though I cannot for reasons previously given trace all of the forms 

 to this variety, it is evident, that in the main proposition, the descent of the Pit 

 forms as a whole from the Neuselhalder and perhaps other Tertiary varieties of Fl. 

 levis, Dr. Hilgendorf is amply sustained. 



More or less doubt must of course hang about conclusions based upon anything but a 

 series of close observations, and therefore I cannot at present do anything more than 

 suggest the probability that this First Period really represents two, one including the 

 Sylvana Limestone and the Coarse Breccia, and the other beginnmg with the Plan- 

 orbis rocks. I am also bound to state certain alternatives by no means improbable, 

 namely, that the remnants of an older fauna as shown in the Neuselhalderhof rocks may 

 have lived side by side with the new fauna for a considerable length of time, or on the 

 other hand, that the fauna of the Sylvana Limestone merely represents an unsuccessful 

 migration from a neighboring fauna, which gained only a temporary foothold in the lake. 

 Both of these alternatives appear to me to be unsatisfactory, but in such a locality nothing 

 but the keenest exploration can settle such a question, and that has not yet been given to 

 this point by any person, so far as I know. 



