3© BULLETIN OF THE LABORATORIES 



old divide easily accounts for the lack of any large tributary stream on 

 the east side of the lower Scioto. 



From Waverly the main axis continued northward along the pres- 

 ent line of the Scioto into central Ohio. At the great bend of the val- 

 ley in southeastern Ross county a considerable tributary was received 

 along what I have called the old Jackson valley. As shown by Mr. 

 Fowke (article II this series) another large tributary was received just 

 above Chillicothe, the Paint creek drainage. 



The course of this great drainage line from central Ohio may be 

 somewhat doubtful but the writer has as yet no grounds for modifying 

 the views expressed in his first article in this series, in which he states 

 that the Preglacial Muskingum and reversed Scioto found a western 

 outlet along the line roughly indicated on the map, Plate V, accom- 

 panying that article. The facts here presented and the conclusions 

 drawn seem also in harmony with the views expressed that the Ohio river 

 valley along southern Ohio has been developed, in very recent geologic 

 time, from the adjacent parts of several older river systems by the cut- 

 ting down of the old cols between these basins. The silting up of por- 

 tions of the old channels during the back high water stage above low 

 neighboring cols undoubtedly determined some of the important mod- 

 ifications. It would seem as though the filling of the northern end of 

 the old California valley may have produced the deflection of the waters 

 across the ridge between Sciotoville and Portsmouth. If however the 

 waters rose high enough to occupy both courses, leaving the area in- 

 cluded by the Ohio, California and Scioto valleys as an island it would 

 be expected that the shortest course would be developed on account of 

 the greater grade. 



7. A PSEUDOCOL. 



In determining drainage modifications it is necessary to locate with 

 accuracy the position of the original col which was worn away in the 

 development of the new system. To accomplish this many things are 

 taken into consideration. The criteria will be quite different when the 

 systems bear different relations to each other, notably when the new 

 system is above or below the level of the old and when the new system 

 is larger or smaller than the old. Without entering into a full discus- 

 sion of this question I desire to call attention to a particular case which 

 has come under my notice where most of the criteria seem to be ful- 



