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. 
