OF PLANORBIS AT STEINHEIM. 57 



I cannot, of course, presume to say that the period of time represented by the 

 Pit Deposits was or was not long enough to allow of all, and more than all the 

 changes which took place in the fauna, but simply point out the fact, that no grounds 

 exist for the assumption that they represent any very prolonged peuiods of time, such 

 as have been habitually, and, in my opinion, erroneously claimed, by most naturalists, 

 as essential for serious morphological changes in animal series. 



Professor Cope's researches among fishes and reptiles, the author's among the 

 Ammonites, and, at a later date, Mivart's work on the " Genesis of Species," have all 

 given a large amount of evidence, which tends to show that vast periods of time are 

 not necessarily essential to the production of new species, or even new generic or 

 family forms. Nor is yet the converse true, that animals which have lived through great 

 periods of time, and many geological changes, are necessarily and correspondingly altered 

 in their organization. The testimony of all paleontologists bears witness to the last 

 statement, but the first requires more proof, and for this I must refer my readers to the 

 authors above mentioned. 



In the chapter on the geology of Steinheim, an attempt has been made to show 

 how great the denudation of the surface of the rocks of the Cloister Eidge must have 

 been, and that a part of it probably took place before and during the deposition of the 

 lower part of the Pit Deposits. The evidence that a great amount of denudation 

 has occurred since the Pit Deposits were formed, would not need to be summed up 

 to any one who had seen the locality. 



The whole area of the circular valley must have been at one time covered to a consid- 

 erable depth by stratified deposits similar to those of the Pits, either resting upon the de- 

 nuded limestones of the Lower Period, or what is more probable, merely abutting against 

 these remnants on the sides of the valley. These have almost entirely disappeared, since 

 what is left adhering to the sides of Cloister Ridge can only be considered as the merest 

 fragments of what the mass originally was. What the vertical height of these deposits 

 must have been is of course wholly problematical. SuflBcient evidence has been brouo-ht 

 forward to show that, though the elevation of the Cloister Ridge took place before the Pit 

 Deposits were formed, this elevation was continued certainly after their deposition was 

 completed, and probably also went on more or less while they were being deposited. This 

 of course, would be an element in the problem, as well as the determination of the extent to 

 which the neighboring heights and the outlets, which once bordered and limited the depth 

 of the waters of the lake, had suffered from sub-aerial denudation. This portion of the 

 problem, therefore, can only be safely approached by a local geologist, and it would be 

 idle for any one else to attempt an estimate. That the Pit Deposits were much thicker 

 than they are at present, and that they present in every way only fragmentary evidences 

 of what the fauna of the lake was, as well as of its geological history, can hardly be 

 gainsaid, unless diflFerent conditions governed in former periods from those which we now 

 find in similar localities. 



It remains only to add that ample provision for the removal of any requii-ed thickness 

 of deposits once probably existed in the drainage of the surrounding mountains. A pro- 

 portion of this even now passes through the valley of Steinheim to the Steubenthal as 

 described in Quenstedt's article previously quoted, and ample evidence of the former exist- 

 ence of a more powerful stream, may be found in the official geological map of Wurtem- 

 burg, " Heidenheimer Blatt," and its accompanying text by Prof Fraas. 



