154 Annals of the Carnegie Museum. 



changes which have occurred since glacial time, more particularly in 

 temperature. In addition he points out that the Naiades of the warm 

 waters in the interior of the state of Michigan attain the same size, 

 luxuriance of growth, and color as they do at the present time in the 

 Mississippi and Ohio Valleys, although their ancestors originally came 

 from the lake. There is, on the other hand, some evidence for be- 

 lieving that they may have come from northern Indiana through an 

 ancient pre-glacial drainage (47), and another way of attacking the 

 problem with which we are dealing, were material sufificiently abund- 

 ant, would be to compare the shells of the interior waters of Michigan 

 with those of Lake Erie. Lake Erie shells are characterized by 

 brighter colors, when compared with their silt- and iron-stained fellows 

 of the rivers, are exceptionally polished, and characterized o therwise 

 in distinction by their well developed lines of growth. Dr. Walker 

 in a letter to the writer (191 4) suggested that a possible source of the 

 depauperate quality of the shells may b* the chemical quality of the 

 water itself, pointing out that the influence of brackish water upon 

 fluviatile species is well known, and there is no good reason why the 

 infusion of the other materials than those in the rivers should not have 

 their influence for good or bad in the same way. An analysis of Lake 

 Erie water furnished through the courtesy of Mr. J. S. Dunwoody, 

 Superintendent of the Filtration Plant at Erie, Pa., is given below, 

 for comparison with that of the Upper Ohio Drainage at Pittsburgh, 

 Pa. (29). 



Analysis of water at 



Analysis of water of Lake Erie Parts per Pittsburgh, Pa. 



■ at Erie, Pa. million. Parts per million. 



Turbidity 3-100 55 



Color 30-40 122 



Iron very little 2 



Alkalinity 105 47.4 



Calcium carbonate 90 56 



Magnesium carbonate 18 * 



Magnesium sulfate 25.5 * 



Calcium sulfate a little 20 



Sodium and potass, chlorides 21.8 26 



Sodium and potass, sulfat es 30 20 



These analyses are corroborative of certain statements I have made, 

 and furnish food for reflection. 



* These substances are not recorded as being present in the water at Pittsburgh. 



