378 NATURAL HISTORY BULLETIN. 



which was flooded. South of the Iowan drift - border the loess 

 is uniformly the superior member, and whatever amount of 

 sand and gravel may appear is uniformly beneath it. The 

 writer repeats: Under what conditions could flooded streams 

 have produced these results ? Professor Wright's answer to 

 this question is entirely inadequate. He is confronted by two 

 horns of a dilemma: Either there were strong currents, and 

 somewhere there ought to be evidences of them in coarser de- 

 posits; or the currents were not strong and the vast volume of 

 water was moved too slowly to accomplish the desired result. 



But there is another feature of the case to be considered. 

 Professor Wright reports that it would take 96 days to carry 

 off 500 cubic miles of water under his hypothesis. If all the 

 loess area in the Missouri drainage was flooded, it required a 

 much larger volume than this, but assuming this as correct, 

 we still have to consider that the combined time required for 

 the rise and fall of this vast volume of water would take out 

 of each year the greater part of the season suitable for the 

 growth of plants and snails. It would leave only the very 

 highest areas exposed for a sufficient period to develop a flora 

 and a fauna, and we ought to find fossils only (or at least very 

 much more abundantly) in the highest deposits. That this is 

 not true is known to everyone who has collected these fossils 

 extensively. But if Professor Wright would take the trouble 

 to investigate the subject in the field he would know that the 

 species which predominate in the loess do not live on areas 

 subject to overflow, and that the condition which he pictures 

 would be unfit for such species. Professor Broadhead's com- 

 ments on the snails are quite as unfortunate. On p. 394, 1. c, 

 he says: "On every wreck heap I would find among the trash 

 hundreds of land shells, mostly Helices, and sometimes the 

 small Pupa, all being landshells, and rarely did I find a Plan- 

 orbis or Lymnea. The Succinea I could also find. These 

 shells are also found with the loess. Those in the river were 

 washed down from the hills by the rains, and the shells in the 

 loess came the same way." In the first place it is fair to call 

 upon Professor Broadhead for a bill of particulars. The term 



