154 NEWER PLIOCENE PERIOD. [Ch, XI. 



and Lorraine, which were previously composed of barren sand 

 and gravel. 



The perfect state of preservation of the land-shells in the 

 loess may have arisen from their having been floated in the 

 turbid water in which there were no hard particles to injure 

 them by friction. The occurrence of fresh-water shells is so 

 rare as by no means to warrant the theory adopted by some, 

 that the loss was formed in a lake instead of having been 

 thrown down from a transient flood of muddy water. A few 

 individual shells of aquatic species, the inhabitants, perhaps, 

 of rivers or small ponds, may easily have been washed away 

 and intermingled with the rest during the inundation. The 

 names of fifteen species of recent shells, which I collected from 

 the loss, are given in Appendix II.* 



* M. Bronn of Heidelberg possesses a more extensive collection. 



