BOUNDARY OF THE GLACIATED AREA. 153 



In Pennsjdvania it is interesting to note that the Alpine 

 plant Sedum Rhodiola, long known to exist in the narrows of 

 the Delaware River south of Riegelsville, marks the boundary 

 of the attenuated border in the extreme east. Thence the 

 line skirts the Triassic areas on the south side of the Durham 

 Valley, just south of Bethlehem, turns westward to the Schuyl- 

 kill at Berkeley a few miles north of Reading; thence north- 

 ward on the east side of the Schuylkill River to Shoemakers- 

 ville and going over the Blue Ridge Mountain in a zigzag 

 line, passes through Jacksonville and Kepner to Tamaqua 

 where it crosses the Schuylkill. Thence running westward it 

 crosses the Little Schuylkill at Wetherill Junction four miles 

 from Pottsville depot, thence westward through Ashland 

 and Shamokin to the Susquehanna River a few miles south 

 of Selin's Grove. West of Pennsylvania this attenuated 

 border assumed greater and greater proportions, attaining its 

 largest extent in northeastern Kansas, from which fact the 

 deposits have been denominated " Kansan Drift." From the 

 thinness of the " Kansan" deposits and their more highly 

 oxidized condition, this drift has been assumed to be vastly 

 older than the deposits marked by the terminal moraine of 

 Lewis and Wright and, unfortunately, have given name to the 

 whole attenuated border and in popular apprehension carried 

 with it the assumption that they are all synchronous in age. 

 With this protest, however, it will be best to continue the 

 use of the term and speak of these deposits as " Kansan" 

 and of the latest ones as " Wisconsin." 



One of the most impressive facts ascertained by Professor 

 Williams concerning this earliest advance of the ice over the 

 region between the Lehigh and the Susquehanna valleys was 

 that of the formation of an ice-dam across the mouth of 

 the Lehigh at Easton, producing a temporary lake (which 

 might properly be named Lake Williams) extending from 

 Allentown to Topton and there overflowing into the Schuyl- 

 kill at Berkeley a few miles above Reading. The depth of water 



